The market seems to be too small for such. But let me share that we took a 486dx100 with 8 megabytes of RAM, an ISA modem, a network card, video card (no hard disk) and booted up Freesco. It worked.
My bet is that you can find the needed parts to make your own.
I am trying to set up my home network and I have dial up ISP. Live out in the sticke far enough that cable/dsl may never make it.
Does anyone make a router for dial up?