No carriage bolts at all, or just none in the size you need? I don't recollect seeing anything smaller than 1/4-20 ever.
Pop rivets would be cool, but you got her done now. Looking good.
Plenty of normal sized carriage bolts, just nothing down at the #8-32 size that I am using.
I considered pop rivets, but I just decided they aren't right for this contraption. I need more adjustability to get all of these very odd pieces to fit together.