Simplest way is to save up 200 gil and go to the Clan Outfitter for Clan Centurio (Muthru Bazaar, Rabanastre) They can also be obtained as rewards for Hunts, and as Loot from some enemies (particularly if you rack up a ridiculous Chain, something above 30 or 40. Above 50 and you're almost guaranteed some.)
Specifically, which enemies give out teleport stones? I'm at the Nam-Yensa Sandsea, going to the Tomb of Raithwall.
Although Teleport Stone doesn't seem to be there at the moment, check out Final Fantasy Wiki: Loot (Final Fantasy XII). It might help, especially if I missed it...
Long story short, you can get nearly anything from a large enough chain.
Your best choice: go hunt down the Urutan. Get as high a chain as you can, you'll make a killing in Loot, and probably get yourself some helpful stuff like Hi-Potions, Exp, LP and Gil, and those Teleport Stones.