It must just be Purina, Amprolium is not included in the VFD as it is not an antibiotic and does not create immunity issues.
If anyone really needs to purchase an antibiotic for their birds, I would suggest you look at aquarium medications, most of those are still legal. I bet meds for pet birds are still sold too. Those all have higher costs (avoiding any reference to a profit motivated conspiracy here) but still much cheaper than a vet visit in the quantities we require.