You can use after market springs, but it requires knowing how they work.
To use the previous example, if the trigger/mainspring were changed to a lighter one, to try to reduce trigger weight, the recoil spring might have to be changed to a heavier one so that the gun continues to work.
Change one thing and other things are affected.
For the cz and some clones, the czcustom shop should have info, as will EAA for their similar Witness models.
http://czcustom.com/
http://eaacorp.com/