You might try
Desert Harvesters and see if they can either supply or point you in the right direction.
[EDIT] On further reading, it looks like they're not selling seed or
trees right now and they appear unable to respond to individual queries. Native Seeds/SEARCH would have been my next suggestion, but I don't see seeds on their website. Just flour and pancake mix.
Best bet would be to find someone in Tucson who can pick some for you this summer. Just make sure they know how to spot the native species.