By glowring, I'm assuming you mean a tritium glowring.
Here are a couple sources from fellow CPF members.
This or
this is probably what you're looking for, the first is a sales thread run by Merkava and the second is a thread run by taegle. both are for commercially produced tritium glowrings
Merkava also makes and sells
these, which are smaller and slightly brighter, but are covered by silicone
If you want small and bright but don't want silicone coating an alternative is to buy an acrylic tube from Leslie,
at this thread, and buy a tritium tube from
taegle or
b@rt
Leslie also sells
non-tritium glowring made with glow powder from glowinc. Initially they are significantly brighter than tritium, but they will dim over time... if you get the V10 green, they will stay clearly visible for longer than a winter's night though, so they are very effective.
Atomic chicken also makes a
glow fob, but he's in the middle of moving his business so you would have to wait a while to get one.
... i think that's it for sources... there may be some other people that sell tritium vials, but the people above are who popped into mind first.
I own a nite glowring from Merkava and several glow powder glowfobs from Leslie. I would highly recommend both.