Retro have it on their website but do not sell it. I have searched high and low for a supplier and the bottom line is, I don't think there is one.
I have to get mine from B+S in the States. In the short-term I have a few grams you can have to give it a go, but perhaps if we meet up soon we can arrange some sort of group purchase. I am running fairly low on PD and NA2 so will need to make a (painful) order sometime soon. (Have to be after Xmas, I fear though.)