When TDP came in, each EU Country was allowed to "Gold Plate" the basic legislation if they wished. Some countries added further restrictons but the UK didn't. The UK allowed a grace period when old stock non compliant stuff could be sold legally in this country.
The "normal" GS sold in the UK was the slim job which I always doubted held what it said, but on the Continent, in Spain to my certain knowledge as I bought them, the iStick 40w TC was sold as a kit with a totally different shaped tank similar in appearance to a D22 Zenith, but bottom fill. According to the bumf which came with it, it was specially designed for the iStick and supposedly able to run on TC - remarkable as I could never find TC coils for it!
I did always feel that that tank held more than the normal "Slim Jim" version.
Yes you can buy oversize kit from China, if you are prepared to wait for it, work round the fact that Fasttech can't now accept readily Paypal and know how to get round that, and can be assured that you wont be paying Import VAT now.
Hope this helps ...