Pink insulation from HomeDepot or Lowes will work great for an enclosure!! No need to get Rockwool or 705. Just wrap the insulation in a nylon type cloth to keep the fibers from blowing out of the port (if it has one) or from getting into the driver. The acoustical benefits of regular insulation are even better then the widely used Polyfill. All though Polyfill is a good alternative & there are no extra steps to be taken, as in the use of nylon. I've used both & they both sounded great.
So if you can't find the Rockwool or 705 then just go the convenient route of insulation or polyfill.