Use thin epoxy, like the self leveling type for pouring bar tops. Use epoxy dyes, as the use of model paint can make the epoxy improperly harden sometimes. The tubing can be found at hardware stores, model shops, hobby shops, and online. Like mike said, it is best to go where you can test fit the pieces.
Here's a great trick:
If your name is a mirror image letter ( A H I M O T W X) you can make a mosaic rivet with your initial in the center. It may take some creative pre-assembly, using super glue or tacking he parts together at the ends with solder, but once in the tube and resin filled, the effect is stunning. For example, My "A" is made from a "V" channel that I squish a bit and trim until it fits the round tube. Then I trim a piece of flat to fit where the cross bar of the "A" will be. I put the "V" in a bed of modeling clay to hold it, set the cross bar in place, and apply a few tiny drops of super glue to hold it there. Once set up, I slip the "A" in the round tube, mix the red resin up, and sock it up the tube by putting a piece of plastic tubing over the end. When the epoxy is about 3" up the tubing, I remove the rivet from the epoxy cup, quickly plug the end with a little ball of modeling clay, and hang it from the tubing to dry.
Stacy