Dunno about the source list, but I have found kitbuilders and small parts suppliers I never heard of at the Narrow Gauge Convention which you can get into with a day
pass. Unfortunately, that is a once a year occurrence at wildly various parts of the
country. The O scale show in Chicago has, for me, been less rewarding and still
farther down, the one in the Indianapolis area. The one or two O scale shows I managed to get to in the NE have been more rewarding, as closer to more of the kitbuilders?