I would just pull into a NAPA, or similar, buy the parts, park the truck off to the side, and have at it. If there is any question, tell anybody that's bothering you that it's an emergency, you nearly went through the last light, and found fluid flowing out of the caliper.
I was towing a travel trailer through Bangor Maine one summer, when a front brake pad decided to separate from the backer, and leave the scene. I did exactly what I suggest, and nobody cared. The other good part of that plan is that you are right there when you discover that you need some additional part to get the job done.
This would be my advice. If anyone hassles you explain that it was safer to do the job in the parking lot than try to go elsewhere and you had difficulty finding a facility that was willing to do the work.
BTW, is there any such thing as a "quick" brake job? :B
