I tried 3 local pet supply stores (PetBarn, PetStock, PetQuarters), they don't sell it & 2 local vets, both said they wouldn't sell it to me without a consult. Apparently the reason for the vet visit is that that product is not registered to be used for guinea pigs (mainly cattle & sheep) therefore requires a consult before it can be sold.
Also saw this info (broken link removed)
Also saw this info (broken link removed)