accel
Member
When I needed them for my level 10s I always ran Hyjal Summmit on all my toons. The raid zone has Ancient Gem Vein that have a good chance to contain Talasite. You can only run the raid once a week, but its definitely worth to run it on all the toons you can.
Two raids that are even better:
Magtheridon's Lair - the only boss drops a bag with gems, these can be talasites
Sunwell Plateau - trash mobs drop gems directly, these can be talasites
I got many more talasites (and gems in general, but gems in general are kind of not needed because you can buy analogs - with some exceptions - for marks of honor) out of these two than out of Hyjal.
Also: veins in Hyjal don't seem to respawn at all. Initially I thought they might. No luck.