Try different Purina dealers. It shouldn't make a difference, but it does....I used the same frustrating vendor for 18 months, never reliably received my order, finally tried another about 10 miles further out. They've been great, I now get my stuff in within a week, even got two bags of AM Largemouth within 2 weeks of ordering, and I know they had to special order that. I drive out of my way to buy other things there now.
Most feed stores get orders in from a central distributor on a weekly or more frequent basis. I know that both stores I've tried order from the same distributor, so all the excuses I got previously were just that. Sounds like your store may just not be interested in really being helpful.