As far as I know, there is nowhere that sells it in the uk. there used to be a company in the south somewhere that advertised it's own version, although noone could ever work out if it actually was the pyrocat HD that Sandy King came up with
I have not found it anywhere in the UK either so have switched to exactol lux which, apart from the shorter dev time, gives pretty much identical results and keeps better. Apparently Prescysol is also very similar though I have not tried it.
Silverprint have "pyro" developer http://www.silverprint.co.uk/chem34.html
I'm not familiar with pyro developers so I have no clue if that's what you're looking for or not. Silverprint is close to Waterloo station, though, so it's fairly convenient for London. If you can find the formula to make your own, Silverprint also stock the chemicals to make it.
I went to retrophotographic and got raw chemicals, salter diet scale etc for price of about 3 lots of pre-prepared developer. Got masses of it left which ought to last me a significant amount of time.
It is very easy to mix up. I tend to do small quantities due to my low volume use.