Getting s12 parts

I'm getting a 1988 Nissan 200sx xe for around 900 but its not in the best condition but I live in California so its understandable, the only big problem that the car has is that the water pump doesn't work so the car overheats. I've been looking around for aftermarket things that I wanted to plan on buying but Im having trouble finding a lot of parts online. I just wanted to know some websites that have good aftermarket parts. Any help would be appreciated. Im just getting into this community so I thought posting might help.

You have to understand what you're getting into. Essentially there's no aftermarket support for the S12 platform.  Find a water pump on RockAuto

Welcome! What motor; is your car still stock?
Rockauto is a good parts source and you can still find alot of stuff at your local store as well.  If you are doing the pump, do the timing belt and tensioner as well.

Welcome.  Not much factory replacement parts available for such an old car let alone aftermarket parts.  Do some research on this forum and you should be able to find something from the z series like bushings and brake pads that will fit the s12.  I would check the conditions of the radiator and your accessory belts while you're at it beside doing the timing belt and tensioner.