Does such a beast exist? I'm joining a side acoustic project and they want me to play an acoustic bass. Obviously there are many of those, but I thought it would be cool to do an upright. I have a fretless at home that I mess around with, but live, I'd be way more confident with a fretted instrument.
Honestly, just do what all DB bass students do. Take a nice No. 2 pencil and draw frets on the area where you need them. Sheesh.
Total joke. At least the bass violone (say vee-oh-LOW-nay) has moveable gut frets. When the instrument changes shape with the seasons, which even laminated uprights do, fixed frets will not work. All of the Viol family abandons (movable gut) frets in the upper positions. They just don't quite work on a large acoustic instrument. Heck, upper register frets barely work on electric bass, LOL! Then there is tuning to an ensemble...
Just practice on it a bit, and you'll be fine. I got a gig playing jazz 2 weeks after I bought my first upright. It was a trial by fire, but I muddled through. Destroyed my hands for a week afterwards, so if you can find a teacher to iron out the gotchas at the start you'll stay healthier. At least dig around youtube for basic upright bass lessons as the ergonomics are different from what you're used to and you can injure yourself if you attack it the wrong way. But the notes are all in the same relative places so you'll be fine after an initial breaking period. I played with an inline tuner for the first year too so I could keep an eye on my intonation as well as an ear.
What about something like a solid body bass violin but a lot smaller, shaped a little more modern, like a Strat but bigger. You could use thicker strings so it would be lower register than a guitar or violin.
If you’ve put in some time with a fretless bass guitar already, you should find intonation on the upright is actually easier. The longer scale length means the same absolute error in position causes a smaller error in pitch, and the tubbier sound makes it harder to hear pitch errors. Just dive in, you’ll be fine.
In addition to the historical violone, there have also been fretted EUBs marketed from time to time. And i don't think that's too bad an idea since holding the instrument upright is just generally more ergonomic than holding it like a guitar. My son had a 1/8 DB for school, with a 32" scale, and it was a real dream to play, I never played an instrument of any type that felt so comfortable. The problem with these things when they come around is that the marketing would go something like "it has frets and you can bow it", but that's dumb because learning to use a bow is a much bigger hill to climb than learning to play fretless - and then you try to learn to use the bow and realize it's trash on metal frets without vibrato, and the whole idea was just a scam. But it's still kind of a good idea, if you could convince BG players that it was more ergonomic, comfortable, etc.
Use painter's tape, cut in 1/8 inch wide strips, and tape them to the fingerboard where the intonation points are if you simply cannot take the time, meaning a few hours and a few sessions with a good teacher, and substantial practice, to learn the rudiments of Simandl positions, and get the nut in the proper relation to your temple so everything is by muscle memory. Many jazz band/swing band charts in flat keys can be played well in the one-half position, with extension to the other positions occasionally as necessary, and most string band songs in sharp keys can be played well in first position, again, with extension to the other positions occasionally as necessary. Oh, yes, the frets:
NS does indeed make a fretted version of their Omni bass. The Omni is basically a 34" scale bass with a radius suitable for arco playing. If you scroll through the images on the page below, you'll see what the fretted one looks like: CR Omni Bass | Ultimate Form, Function and Performance | NS Design
the answer is yes it technically exists in various forms. the obligatory part 2 to this answer is that there's definitely a reason why you don't see them ever. Baroque fretted-bowed-string instruments are one thing, and the voice they have is just significantly different than the type of sound you are probably thinking (acoustic bass guitar but a lot bigger)
Questions: Are all the "acoustic" project players performing without pickups, mics, and a PA? Do you plan on amplifying (need pickup and pre-amp) or putting a mic on your erstwhile upright? Are you aware that even in a bluegrass ensemble, typically sporting guitar, mandolin, fiddle, banjo, upright, and 3 voices, the bass is essentially buried playing unmic'd? Have you ever tried an "acoustic" bass guitar (ABG)? My advice: ABG is not a viable instrument unamplified, even IF everyone else is unamplified, IME. Upright, AKA, double bass (DB) is great, and I encourage anyone to learn it. However, let's just say that to play DB as well as you can your electric is what I would call "a non-trivial challenge." A workable upright, set up, bag, spare strings, pickup, and preamp will set you back at least $2500, and the sky is the absolute limit. Don't forget your bow, rosin, books, lessons, and large vehicle to fit the upright, with you, your amp, and room for a stool and music stand and stand light—and better bring an electric as a backup. I've had disasters, like the time Sam H. drunkenly pushed a speaker column over and neatly severed the neck off my upright that was resting on its side nearby. I've broken strings, and had pickups just quit. Bridges and sound posts can drop. Don't mean to scare you, but it's not just a big electric bass with no frets. It is a vastly different instrument. Just say no. Bring the fretless.
How is this "acoustic?" Not snarking, and NS makes some nice stuff, but a fretted 34" scale omni is just a fretless bass guitar.