You can use SRAM cache ICs from old 386, 486 and first Pentium motherboards. Look at their part numbers and then search the Internet.

The reason *I believe* there is no 64kbyte memory chip is as follows: suppose the minimum geometry is 0.40 um (micrometer), when the fabs are capable to reduce it to 0.20 um, in the same die they can get four times the transistors as before. You can see the evolution in SRAM ICs: 2kByte, 8kByte, 32kByte, 128kByte, ... same happens with DRAM ICs.

Regards,
Enrique.