Moog Music is so small that it's a miracle it's evin still around in an age when just about everything, if not all of what we use today is made by outsourced (slave) labor.
The reason the Pro is nolonger available at Moog Music, likely has to do with the fact that as of last month, only 80 Pros were going to be produced this year. Some of those were likely spoken for, and the remainder are to be sent out to music vendors who had working contracts to recieve a given number of them. (speculation). So, they just don't have anymore in house stock.
I'm sure it might have been easier for folks in the U K to use Moog Music's site to buy from, but there are plenty of online vendors who ship internationally, and are quite reputable. Hopefully, there are vendors in the U K who will try to stock a few remaining Pros.
To set your minds at ease, especially for our friends in the U K, I can't go into any details for now, because finallized designs have not yet been selected, but plans are in fact, in work for the pro's and standard's successors, so it's reasonable to assume that sometime within this year, or next, the U K can expect to be able to get high end theremins through Moog Music again once production gets underway. As soon as I, or thereminworld know something, everone will know.
Keep in mind, that the Etherwave Standard remains available through Moog Music for the time being.