Sadly, this will really require parametric search capabilities (like what is offered at Partminer) - RTC chip, made by Sharp, DIP-24 package. If it exists other than a one-off. Tough stuff.
- Stiletto
SDIP-24 package, not DIP-24. note the pin spacing.
Edit: could it be an MC146818 clone (same rtc used in ibm at)?
LN