When I got my first unlined ESP fretless neck in the late 80's, it was unfinished.
The first thing I did was go to Radio Shack and bought some of those dry transfer rub-off letter packs that were used to label electronic equipment. They had little 1/8" long lines in those packs you could rub onto anything you wanted.
I used a fretted neck as a template, and rubbed off lines on the side of the neck where frets would be. I then rubbed off dots between the frets, where they would normally go on a fretted bass.
So, from the side, it is lined, and looks like a regular bass. I never understood an unlined fretless having fret dots at the actual fret positions, it's not standard and it threw me off. Seemed stupid and non-intuitive.
I then sent the neck off to Pat Wilkins to clearcoat the entire thing. It came back perfect, but the fretboard was so flawless I never wanted to scratch it with strings. It looked like fine furniture.
To me, that's how an unlined fretless should be, and I'm surprised no one makes them like that. Lines only on the side of the neck indicating where frets would be, and dots in the normal places on the side of the neck. The fretboard itself can remain blank.
If someone else makes them like this, I am unaware of it.