I hate to burst your bubble but there are no alternative methods, preorder weapons are only receivable through the codes you get, so either trade for it on here/buy it on eBay, P.S
You may want to re-consider trading The Inquisitor for The Channeler, I have both maxed and I prefer the inquisitor, Their bonus's are: The Inquisitor: Drains life with each hit, You gain gold with each hit (Helps out early on), The Channeler: Improves the damage of your Shock ability, and Improves guild seals gained in combat, they both do the same damage with each melee hit though.