I would have expected a response to my question on practice tyres, but have not had one yet so I'm going out on a limb.
In the AARCMCC rules there is nothing to say that you have to buy practice tyres from the host club or that practice tyres are controlled. That said, if you go to Hobby Habit to buy the same tyre set, you will pay the same price as what the club is selling them for (I didn't come up with the pricing). So, there is no difference in cost to the competitor if you buy them from the club or not, but if you order them with your entry you will be guaranteed to get some as I'm not sure what availability is likely to be from shops if people want to buy them just before the event.
Just remember that as they are pre-mounts, you will not be able to do ANYTHING to the tyre set as far as holes go.
Also, make sure your entries are received by Friday. Use Express Post if you have to get them here from interstate if you need to.