Cured dry rock is kind of an oxymoron. You can not have cured rock that is dry.
Curing is the process where the rock is put in the saltwater to acclimate or condition the rock for use in the aquarium. This process builds up the bacteria and such to make the water usable in an aquarium.
If you want to add dry rock, you can, just rinse it really good first. Just make sure your system is stable and been up for at least 6 months. Add small amounts at a time or you may get an ammonia spike.
Cured live rock is ready to put in without having much effect on your system. It already has much of the bacteria and macrobiotic stuff that keeps it from causing system spikes.
For cured rock, check Discount Aquarium in Tempe. One of the least expensive.
BOb