I just went to Fry's in Sunnyvale and was able to get the gamecube adapter. They have 15 left in the store. Check their website to see if your local Fry's has them. All three Fry's near my area have them in stock.
I have a $5 Gamestop online giftcard I'm willing to trade for Microsoft Points or Xbox Live Gold. Wanted to trade earlier, but didn't realize you had to wait a few days after registering in order to post. PM me if you want to trade.
Edit: Traded the $5 Gift Card