Hi Greg. Hey, I got your email...sorry for not answering, been so busy...but actually this is better here, we like to keep things recorded and searchable for others who may have similar questions.
If you have a local hackerspace or a TechShop-type of place, they may have a laser cutter available for members (maybe even non-members, with a reasonable donation). Or you might find a local hobbyist with a laser cutter...ask around, post to Craigslist, etc.
I've attached an Adobe Illustrator (v10) file that's a template for four triangles (you'll need 20 triangles total) plus the little hanger/strain-relief thingy:
Barring that...if you can live without the slick mirrored finish, and if you have some power tools (bandsaw, drill press), the triangles can be cut from Sintra (aka foamed PVC), which you might find at plastics or sign shops. When making multiples of something that way, I'll usually stack up several layers (joining them temporarily with rubber cement, which peels off later) and drill and cut as a set.
Pre-loading data would be a good idea. The Time Ball I built used XBee, and it was *barely* reliable enough to work as long as the transmitter was within a few feet. Triggering fixed sequences over XBee would be a bit more robust, but wired over USB is still likely to be best.