Rich writes:
The 8101 dual-port 256bx4 RAM is no longer available,
but Jameco has a 5101
which looks like a likely sub.
Check the timing specs; the 5101 might be slower.
Also, 8101 is just a different marketing designation for 2101, just like
8702 for 1702, etc. The 2101 should be easier to find.
Apparently Intel's marketing people didn't think that engineers would be
able to figure out that their standard RAM, ROM, PROM, and EPROM
products would work with the 8080, so they introduced 8xxx-series part
numbers for them.