Is there a lower limit on operating frequency of CMOS SRAM?
No, there is no minimum frequency because it's static RAM. Any digital circuit that's described as "static" doesn't have a minimum frequency - it can operate with all signals held static for an extended period of time, hence the name. "Dynamic" circuits have a minimum frequency.

Just because your circuit operates at a low frequency doesn't mean you can ignore all timings, however. You still have to meet the required setup and hold times, as well as the maximum rise and fall times. The latter usually aren't a problem if you stick to a single logic family and don't use 4000 CMOS. (74HC/HCT/LS will be just fine.)