I would try ebay for sure, I always find crap there. If they don't have it selling, most times if they are parting on out they have it ready to be posted. Also some salvage yards across the US have it, DVAP.com for example. Look at galaxieclub.com in the members classifieds or even business classifieds.
ha ha ha, .......... i actually found and bought one on ebay..... but it was my luck that i assumed it was a 2 door galaxie and it ended up being a 4 door, so the SOB doesnt fit.... it is also the seller fault for never putting it on the auction.