Another option is the InMOS IMS1203 CMOS SRAM. Same pinout (it's a
JEDEC standard, so other examples probably abound), fast (45 nsec)
and low power (80/15 mA active/standby current).
Shame that you need the 4K parts. I have a whole potload of the 16K
20-pin parts.
FWIW,
Chuck