I agree there needs to be a way to get them, I've sent my retainer on so many ventures and haven't gotten a single pot of special dye back. And what if he brings back one that I don't even want? They made them purchasable with Gold Chocobo feathers via the Recruit a Friend campaign but still, not everyone is capable of recruiting others. Not to mention, my boyfriend who recruited me still has not received said Gold feathers and neither have I received my Silver ones.. But I digress...
Buying them with MGP sounds like a good idea. The MGP prizes need a boost. They're all mostly kind of lame.