Which engine did you have ??
The one should only run when the temps get up to around 220 deg then at 230ish they both come on. Ir when the AC is on they both should run.
If one constantly runs then you have other problems, could be a relay or the temp sending unit isnt functioning properly.
Their's many palces to get after market fans.
Best way to find them is measure your old units then start searching the web, ebay, etc etc.
They do need to be the same voltage(s) and amps, other wise you'll need to upgrade your wiring and relays.