Hi,
Although Paulr has made some clarification, I have to say some other things.
The sale/import/export of radioctive products is strictly controlled in the US (not sure of Canada). Even it is embedded in an instrument (watch, compass, etc.) it still needs to be legislated at the first time of import/manufacture. Try to order a small glowring over the net, an official retail won't work. <img src="/images/graemlins/frown.gif" alt="" />
I doubt any beta lights, glow rings, tritium map readers would go through regular customs. In most cases the well informed manufacturer, or the carrier will deny to ship the product to the USA. And the local manufacturers are not allowed to sell any of those to non-industrial/non-military customers.
Of course you can buy those through ebay, or ask a friend to bring home from Europe, but you should take care to avoid at all cost any commercial-looking quantities (e.g. 20 tritium map readers). In today's terror-concious air travel/transport I don't wish anyone to explain radioctive sources in his/her package.
As I've previously stated, the large tritium light sources are outdated in most survival cases. I still recommend some led+lithium.