A Youtube scratch build creator I've seen a few videos of uses dollar store plastic diamonds for rivets on vehicles and buildings. Just a dot of glue and apply with tweezers. Not sure how the size will compare since I haven't yet bought them myself, but they might be a cheap option for the armor rivets.
Yet another Youtuber I've watched carves spare sprues into a mostly circular shape and then slices off bits for rivets. If you use this method it won't be as even, but you can control the size more easily. Free except your time and effort plus glue and you have full control over size and shape.
Youtube scratch build creators are an excellent source for ideas since you can see them in use. Automatically Appended Next Post:
If you're looking for heads and shoulder pads to match, Pop Goes the Monkey on Shapeways has a wide variety of SM
conversion parts. https://www.shapeways.com/shops/popbits?s=0
I can't personally vouch for them yet, but their items look good in the pictures. I want to say Spikey Bits is how I first found them, but I can't recall for sure.