There are a few old posts on this but the problem remains... where can you get or how can make 4 strings bass set for the ultra shorties... 24.75" Kay Value Leader Bass, 25.5" Supro Pocket Bass or even some of the 28.5" scale basses. Problems is you need real fat ones for any kinda tension on the shorties. LaBella does not custom make anything like this... I guess 'beggars can't be choosers' in that bet anything out there is are rounds, and I am all about flats. just chopping ones too long, you can't get them thru the little cheap tuners on those things. You would need like Pbass tuners... It doesn't have to look pretty, tho.
The Ibanez Mikro and the Jackson Minion, both 28.5" scale basses, can fit nominally short-scale strings with a 32" winding length ball to silk/taper, if barely. The Fender P-Bass Jr., same scale, had string-through-body loading, so it also could accommodate commonly-available short-scale strings; its successor, the new Squier Mini Precision, has no string-thru and less room between back of the bridge and E-string tuner than the Ibanez and the Jackson, so one has to settle for winding some of the fat part of the E string on the tuning post (though there are a couple light/normal gauge sets that appear to fit fine).
As for guitar-scale (24~26") electric basses, both old and new:
1) these puppies (La Bella/Gold Tone MBLS)
MicroBass LaBella Flat Wound Strings | Gold Tone Folk Instruments
are essentially a dwarvish version of the Deep Talkin' Bass Flat [Invalid or Expired Link Removed] set (gauges 49-69-89-109) and appear to be exactly what you need;
2) for those who like regular strings (steel-core, roundwounds) and big gauges in order to get familiar tensions on a supershort-scaler, Fernandes Guitars still sells the accompanying set to the original, 24" scale Pie-Zo (a.k.a. Nomad) Bass. The set is called PSZ-2000 (gauges 65-80-105-125) and can be found on eBay, including but not limited to
here (possibly also through their US importers, Gear Street: the set is not on their
website though, one'd need to contact them to confirm if they can get it from Japan).
Newtone Strings in the UK and Pyramid of Germany do custom work; alternatively you could try and contact Stringjoy, Curt Mangan, Black Diamond or some other small-size company that is Stateside.