If you're truly talking about SRAM, there aren't too many places around that still carry the stuff. COAST sticks and individual cache chips are no longer carried in general on the internet, as these haven't been used for over ten years.
If you're looking for some SDRAM, eBay is indeed the place. SRAM (Static RAM) was used in early Pentium days on COAST sticks as the form of L2 cache back in the day. SRAM is still used, it's now called L1 and L2 cache and it's only typically used in smaller amounts within processors. SRAM chips were included on the processor's PCB for Pentium II and Pentium III SECC processors.