I've called 5 shops, and this is what I recommend:
1. Try Lee's Cycle. They'll swap shims, but when I checked they were out of 255s, in the 29.5mm shim diameter. Kontiki, Stark Cycle, National City Cycle, and Fun Bike Center all said they don't swap shims or only had 29mm shims.
2. If you want to buy some shims, Stark Cycle ordered the size I needed, and only charged $5 each, with a 2 day turn around.
Hopefully this helps those San Diegans trying to hunt down the correct shim sizes.