Which UK supplier would that be? The D-Limonene tek does indeed look promising, however I've not had any luck looking on eBay and wasn't able to find a reliable source. Also looking at the tek, about 75ml per 80g of bark, since SWIM has to extract ~800g, around 750ml of D-Limonene might be required, which SWIM expects might be very costly. Furthermore, SWIM would require 11l of water, which is quite unwieldy compared to one of the simpler STB teks.
SWIM's also looking into various brands Panel Wipe as a naptha substitue. The problem with Bartoline and other substitutes wasn't that it didn't pull spice from the solution, but rather that due to its higher aromatic hydrocarbon content it actually dissolved freebase better thus making any freeze precipitation a lot less efficient, and at the same time didn't evaporate anywhere near as fast as naptha, thus making reducing solution volume for better freeze precipitation or even simple evaporation a problem.
By their nature panel wipes should evaporate very quickly, and without residue, however none of the brands on eBay have MSDS links or anything
SWIM might have to check out local paint shops or B&Q or something.