Mark Garrity would be my first suggestion for something of a full custom nature. We have plenty of top notch leather crafters here on the forum but most are in very high demand and their backlogs reflect that. As QK said, if you're truly set on a full custom rig then it's possible but the cost and waiting period may very well be greater than what you're willing to endure.
Anyway, drop Mark an email (he says it's the best way to contact him) and see if he can come up with what you're looking for.
http://www.garritysgunleather.com/