Darren, If worse comes to worse, you could contact a gun shop in El Paso and alert them to the fact you were having powder shipped to them and would be picked up by your outfitter. Then have Powder, Inc. or whoever you want to that ships small quantities of powder to ship it there with the notation on the package to hold for so and so. But, hopefully, there is someone in El Paso that sells powder.
Sounds like an extensive Google search is coming on for you. And, you can surely simplify your life by just using one grade of powder for both priming and main charge. The difference in ignition time is difficult to notice, especially with Fffg.
And finally, have a fantastic hunt and we will expect one of your wonderfully crafted stories, along with some photos of the event. Please.
John (Bigsmoke)