E-Bay is probably your best bet, although patience may be required. Here is one that already sold. Just conduct a search and "save" it. You will get an e-mail every day for 6 months if the desired part shows up:
http://cgi.ebay.com/ebaymotors/Suzuki-LT185-185-ATV-84-Carb-Carburetor-098341_W0QQitemZ110419751340QQcmdZViewItemQQptZMot ors_ATV_Parts_Accessories?hash=item19b587b1ac&_trksid=p4506.c0.m245