Fiero Jon is basically a reseller of Fiero Store parts. Sometimes, from my experience, they are seconds. I had a lot of difficulty in getting a refund.
When I had my 87 repainted, I just bit the bullet and ordered from TFS. I believe some of the rivets needed for the rocker panel aren't available. My paint and body man found those through his supplier, but the anchor point underneath on the pinch weld required a stainless washer as a backup because the pinch weld hole is too large unless you can find the rivets that have the fingers that flare out. The mandrel needed for those rivets is larger than the common home garage pop-rivet gun can handle.
The black nylon rivets are available at Fastenal. They are bad to break when installing, so a kit with just enough won't be just enough. They also need a special pop rivet gun.
