Does anyone know of a U.S. source for the small beta lights? I didn't believe the same restrictions placed on tritium involved the beta lights, but I can't find a U.S. distributor that sells them.

This question comes up regularly on Candlepower Forums. Betalights are illegal in the US but they do sometimes show up on the forsale board over there anyway. For a PSK you're better off with an underdriven keychain coin cell LED light (i.e. use a CR2032 battery with a white led, instead of the usual two CR2016's). It will still: put out much more light than the Betalight with a more neutral color cast which is better for reading maps; have enough runtime for pretty much any situation; cost a lot less; take less space; and not have any legality problems. The shelf life of the lithium coin cell is about the same as the half life of the tritium in the betalight.