I like that system, it's easy and pretty quick to use. Would you use it for every requested item, or in general? I feel like it would work best as a roll for each specific item, which I think is how you did it.
I would be interested in testing the system too, with my group.
EDIT: Just thinking about the system again, I worry it may be too easy to get good equipment too quick. Take for example, the inferno pistol (arguably the best handgun in the game). This would be rolling at automatically a 9+ with the lowest level trader, and 8+ if you don't mind a poor quality gun at that. So just with a small hindrance and the least connected merchants, you already have a 30% chance of the weapon being available. This becomes even easier if you are in a town with a better logistical supply, to the point it is almost 50/50 for a 2d10+10 damage pistol.
Edited by cpteveros