Simplex do list .310 Cadet dies, and although I didn't want to buy anything at the moment, I tried out their website as far as finding a menu of countries, and saw nothing about not exporting.
http://www.simplexreloading.com/
A while back an Australian firm I dealt with, Ammodump, discontinued Simplex moulds on the basis of irregularity of supply. That may have been connected with the death of the founder, just as the American NEI, whose products I liked very much, suffered after the death of Walt Melander. Both were a long time ago, and there is every chance that they have recovered. My only Simplex dies, for the 5.6x50R and purchased around the time aforementioned, are certainly extremely satisfactory.