Like the Doog said....Plastitruct hex rods make excellent bolts.
For rivets...here's what I do....
Use some plastic sprue from any old kit and stretch it uniformly like you would to make an antenae or the like. If you want it bigger diameter,...stretch to the desired thickness but do so slowly to get it uniform thickness.
Get out an old buisiness card. Any will do.
Use a very small hobby drill bit the size of the diameter of the rivet you want but slightly smaller. About half the size of the rivet that you want.
Use a pin vise and lay the business card on a flat pourus object and drill the desired size hole through the paper card.
Cut heated and stretched spure into small sections.
Insert a section through the hole in the card just enough to let a little (tiny bit) through the card.
Take a ciggarette lighter and gently light and flash the flame across the spure poking out of the card for a split second.
Instant rivet with rounded head.
Drill a hole and insert the stretched sprue to the point where the rivet head is in contact and flush with surface rivet mounts upon. Cut off excess sprue.
Take a little practice but very little.
Here's a pic of my measuring hex rod sizes for my Brummbar I'm working on
Here'a pic of a few hex rods (bolts) in place.