I bought acorn nuts off E-bay got like a 100 stainless steel ones very reasonable, also bought the bolts there...i bought the white caps from Scamp man they were pricey compared to the rest...Maybe this will help you out........
Good ole ebay. I'll see what I can find there. I got the white caps and bases from Ace Hardware. They're not exactly like the originals, so I'm still tempted to buy some from Scamp. The Ace ones stick up a little higher and have a textured finish. And of course the base is different as well.
You mentioned buying bolts on ebay as well. Sounds like you're replacing at least some of the rivets with bolts. I'm planning to stick with rivets for now, but I certainly see advantages to the bolts.
Thanks for posting!