Just use a fan which plugs into a disc-drive style power connector.  Formerly very common, probably less so now, but you're looking for an old fan anyway if it's on a 500MHz part;

 

Option B:  try going fanless.  Buy a big-ass heatsink for a Socket A chip, run sans fan.  Sockets 7, 370, and A all use the same mounting dimensions (though supposedly slight height variations exist).