I found out about those small cans after I purchased 25lb. cylinder from koolit.net. That ebay seller also offers a refill kit with the parts needed to connect it.
R410, R410a, Refrigerant Recharge Kit, 28.2 oz. - eBay (item 400193523766 end time Mar-08-11 12:54:32 PST)
Looks like you would just need the can tapper.