I've done all my set so I can answer that one You get em from Columni Hoods (Kaon HM or raid), Columni Gloves ( Taral V HM or raid), champion head, champion gloves with luck from bags or bought with tokens once you are battlemaster. Other options include Off-hand token from False Emperor HM (if you take the offhand blaster that you can't equip and take the mod off) and main hand weapons (Soa Normal or HM drop). You can check which parts have which by browsing the PvP and PvE vendors on the fleet. Also remarkably, there is not a single grade 26 Enhancement that does not suck (e.g. without alacrity or precision), so we are stuck to replacing this slot in all our gear even on the PvE Rakata set with grade 25 enhancements.. which is unfair vs other classes if they don't have the same issue (haven't checked) since they can net more stats on those 5 mod slots. (current stats 1713 cunning with a mix of columni / battlemaster for the 2 parts columni bonus, since expertise yields diminishing returns past 450 or so anyway)