I don’t know if there is such a thing but could you get a 24 hole rim then have it drilled to have more holes? You couldn’t do this with another hole count because of course you couldn’t get the distances right, but in theory you could do it with a 24 hole rim.
Has no one in the world realised that spoke technology has changed and that most GOOD trails rims are only 32 spokes now (10’and 12’ foots drops and all). You don’t need 48 spokes in any rim if you buy the correct spokes. 48 spokes in a 16" rim is more than overkill, its a waist of time and money.
This is my opinion only, but try to buy a good 36 hole 19" trials rim anymore and I am sure you will find that they are almost as obsolete as 8 track tapes.