I had an idea to replace the hard-to-find expensive chips with a new design. Like the 2518 and MK4096. If we use a small Lattice FPGA, we could do the same things as ROMs where we put the surface mount chip between the pins on a tiny circuit board so the form factor is the same. It's definitely more complicated, but with the scarcity and price of these old chips, it's probably worthwhile.
I was hoping to have one layout for all the hard-to-find chips for each package, but even among the DIP-16 chips, there's different locations for power and ground. There might be enough room to have jumpers to select the pinout to emulate different chips. And there's the problem of level-shifting since the FPGAs are 3.3V. So there's some problems to solve, but I think it's technically possible for a reasonable cost.
I'm thinking like $10 in parts for a chip. The FPGA is like $2-3. There's a dual voltager regulator for another $2. There's level shifting which may be as simple as a resistor, or maybe another chip or two. With the tiny size of the board, it might be a possible cost target. If the device was generic enough, it could be use to emulate many chips which could also help to bring the cost down. Ideally it could replicate any 7400 chip in a 16-pin package.
What do you guys think?