its not illegal at all, only industry have stopped it use due to the extra emmisions when compared to the newer waterbased products. small scale jobs can still use solvent based completely legally

i bought mine from a company called romart, based in lye, in the black country, which to be fair isnt exactly local to you

iv bought 8 litres of solvent based mallard green now, and that uses a shite load of all different colours and tinters.

another possible supplier could be the jawel paint group, i know they were still doing solvent based, but my mate who sprayed mine prefers working with the lechler colour scheme, as he uses their waterbased scheme on a daily basis, so knows the products as a whole quite well, thus why i went to romart