Noah,
I think it is nice that you try and please your lady. She sounds like a good girl or you wouldn't try so hard, but it also seems as if you are being given and altimatum. I'm sure that all vegans are not just about PETA and such. Sorry you didn't get the warm welcome you should have but your question, while you didn't mean for it to sound offending to meat eaters, it does. You have a valid questions though and we are all here to help.
Maybe finding used leather or scraps as mentioned would be easiest to obtain. I don't believe roadkill is your best bet as it will probably be spoiled by the time you get it, especially in Arizona. Also even though UKRay apologized he may have a valid point in silversmithing. It does seem to be a similar craft.
I know everyone here would love to see your work and progress and remember we like pics. Please don't shy away.
Good luck, James