I remember searching for this a while ago. I did find a good link to a guy who sells them practically wholesale (like in sets of 100 cartridges or something). They were dirt cheap too. I'll try and see if I can find the link for you but maybe try searching for CO2 wholesale in google or something.
EDIT: I have some leads however it's still not the guy.
Pyramid Air sells them in packs of 500 http://www.pyramydair.com/s/a/Crosma...Cartridges/590
This place sells them too however they ship through UPS so I'd avoid them unless it's your last option. http://www.getintosports.com/product...roductid=16741
Actually that link that you posted is good too. I'm not sure if they're legit however they have a storefront address listed (it's in PoCo if you're wondering). I don't know what it will cost you to get them shipped but try that place anyways.