Its best to stick with OEM if possible.
The Z store and rock auto sells pumps but the former can be pricey, however you're getting a good product for the cost.
I find that NAPA autoparts always seems to have good OEM parts for the Z.
Might be worth calling them. I wouldn't recommend getting a pump from some of the other franchise parts stores... but for the cheap price, it's always a good idea to have a few on hand. I usually always have a spare ready to go incase my pump takes a crap on the road.
I don't know anyone who rebuilds pumps, but I assume somebody out there does. You can get with your local Z car clubs if you have one that is close to you- ask those guys they may be able to help.
All us Z guys are pretty much in the same boat, so its good to help one another out.
Bon