What I have heard is that the winery has specific buying requirements for their other wines before you can get the Rosado or even some of their whites. Something like you need to buy X number of cases of the red reservas before they can allot you a shipment of the rosado. This in part is what drives up the price.
That's correct. Even if you're at the winery, you need to buy 1 case of Tondonia Tinto to get 1 bottle of Tondonia Blanco. 2 cases of Tondonia Tinto to get 1 bottle of a Gran Reserva. That may extend to the Rosado also, but the allocations/requirements may be even higher for it.