Excellent gun just don't ever need a part. Very bad customer service. They do not sell parts rather they refer you to a 3rd party overpriced company, I think it is called Midwest.
Overpriced? Compared to what? Not all gunmakers sells things as cheaply as Glock. Prices seem comparable to H&K or Walther. And mags for any gun can be pricey if Mec-Gar doesn't offer an alternative.
And while it can be frustrating to NOT be able to buy parts directly from FN-America, unless you do something you shouldn't -- like make modifications to the internals -- you'll likely NOT NEED any parts - except, maybe, a recoil spring assembly -- for quite a while: the guns are solid.
Midwest is pretty good and can deliver quickly, and their prices aren't bad. Their prices for FN parts seem right in line with H&K parts. FN will fix it for you if you send the gun in, and will generally provide a shipping label if you bought the gun new.
FN-AMERICA has a great warranty that covers the gun whether you bought it new or used. You don't see that much, anymore. If it was purchased used, expect to pay shipping.
(I've got an FNS-9c, which I haven't shot much yet, an FNS-40 [and a 9mm conversion barrel], and an FNS-40L.)