It's great that you're doing a survey for this... good luck with it.... but, apologies aside, I still think it's a dumb idea. Just not enough demand... Too much overhead for what little profit you may possibly make.
Oh, all of the stores that I've gone to DO stock ink jet cartridges for at least 4 or 5 different brands. And, let's not forget the laser toner...
If you decide to carry the ink for only 2 brands... then your vending machine is going to be useless for the majority of people.... (unless the majority of people own one of 2 different brands, and that isn't the case.) Here:
http://www.staples.com/Catalog...e=Cartridges+%26+Toner
Stock all of those. Or even 10% of those...