pickyourshoes.com
uptempoair.com
flightclub.com
23isback.com
there is a lot out there, but most legit sites cost more. u can do the footlocker, eastbay, etc route, but they tend to sell out quickly.
best bet is ebay (if you can tell difference between fakes and authentic) and by joining a forum like niketalk, which has buy/sell forums using paypal.
one question, why fusions and not signature? i have been collecting for a long time and can help u out if u have questions or need help with telling difference between real and fakes. feel free to pm me on this subject.