#1 tip: Do NOT harvest AFK. You can bet that even if GMs aren't watching for harvesting bots, other players looking for foundations/spellshards are, and will grief you.
Other than that, i've gotten foundations/spellshards off every "normal" kind of node (ore/gem/lumber/bush/den/root) besides fish (lol, didn't try). Harvesting skills do seem to make a difference, and bountiful harvest always helps. Tradeskill AAs can get you 6% rare harvest chance.