Im sure stropshop will get some in. You can email neil from his site and he will let you know if and when. I guess that grit sizes are quite subjective and different pastes/sprays from different manufactures will have various results, again leather or balsa etc will have an impact on pastes or sprays. I use the thiers issard cro ox on a double sided leather paddle strop and I find that I get a nice smooth shave from it whatever the grit rating.
Good luck on your find!