MM,
I'll let you know I've been watching for that size for about a year. No, I won't pay $13 for NOS parts that small.
I decided to build down to 2-56 for those places that 3-48 are called for. Even my BHM Mosquito uses 2-56 hardware to hold the Norvel Big Mig .074 engines on. No loss there for the smaller hardware.
I tried to see what metric stuff may substitute so I can get closer to the optimum/unobtainium 3-48 stuff. From what I researched, it would have to be M2.5, but no T nuts exist. Next size up is M3, but that is really close to 4-40.
So we are SOL except for eBay's golden bolt sets.