I had some issues tracking it down from local used dealers too. A lot of people say it's pretty common, but I suppose that makes it easy for other people to find too. It's also approaching it's fifteenth anniversary, so I suppose it's becoming a retro classic.
I eventually had to give up and submit to eBay and it just arrived today. The cartridge is showing it's age and the connecters were a bit dirty, but nothing a little rubbing alcohol and some q-tips didn't fix.
I managed to find a copy in this store called FX Game Exchange (Here's the site, in case you're interested, also shows locations : http://www.fxvideogameexchange.com)
They had A LOT of NES/SNES/N64/GB/GBC games on display (They also sold current gen games, as well as accessories for older consoles, such as controllers, video cables, and such). Managed to pick up Banjo-Kazooie and Metroid Fusion!
Also, if you want to order online, Amazon or such works too! Also this store might interest you: http://www.gameovervideogames.com/store/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=2561&category_id=4&manufacturer_id=137&vmcchk=1&option=com_virtuemart&Itemid=6
Either way, good luck! Finding a copy at a store may be difficult.