What you're looking for (I believe) is an antenna with an SMB connector.... a very cursory search on eBay suggests that they're reasonably widely available on eBay.
http://stores.ebay.com/GPSgeek has them as a for instance - not recommending him/her in any shape or form, nor am I suggesting he/she is in any way disreputable - merely that he appears to sell what you're looking for.