Premier never really caught on here. I have heard that the company had a lot of management problems over the years and never really had any solid distribution in the States. Ultimately they shut down their UK factory a few years ago and sent production overseas. I read on another forum recently that they are pretty much non existent as a company now and that they recently sold the name to a low end musical retailer who will use the name for their house brand of drums. A sad end to a once great maker of some of the best drums ever made.
I suspect that the pre-international sizes up until '68 really hurt them in a big way in the US. When everyone was using calf heads it wasn't that big a deal because you could get a new skin tucked to the old flesh hoop. Once plastic heads took over, it was a real problem. Remo is the only manufacturer who ever made heads to fit other than Premier itself. They still make them but you generally have to order them direct or get a dealer to order them. How many people would want to deal with that hassle when you had so many great American drum companies? Not that many apparently.
Even though they went to standard sizes in '68 I think that one reputation stuck with them for many years and dissuaded a lot of buyers. Couple this with the management and distribution problems and it's kind of surprising they lasted as long as they did.