I have a mak-90 what spare parts should I pick up & where
is best place to buy them?
Thanks for help!

If you're concerned about having all Chinese parts, Polytech Parts is the place to go.
http://stores.polytechparts.com/

Probably won't need any, but you might keep a new recoil spring on hand.

Does your MAK-90 have the butthole stock on it still? Or is it De-Banned?
I also just picked a milled MAK 90 and had the same thought as you did with extra parts. I am in the process of de-banning it.
What I purchased so far:
Bulgarian front sight
Bulgarian gas block
AK cleaning rod
AK cleaning kit
Slant brake
Front sight post
I have a order with IronWood for a stock set so I picked up a couple of new upper and lower hand-guard springs.
Sling swivel
front sight adjustment base
front sight base detent plunger and spring kit
New gas piston
and broken shell extractor

When I finish de-banning it I will pick up a new recoil rod and spring.
I will say though, this being my first AK and the more I learn about it you don't need many "extra parts" like you do for an AR 15.