You guys are correct. I don't do them anymore. You can contact Tony (aka Tackleberry), he is the new site owner of
http://www.systema-ptw.com/ and he can do it for you. But you will need to send the complete inner barrel assembly with hop-up to the U.K.. It is worth it, but will be a couple weeks and a couple dollars.
In case you were meaning the motor mod, yes, Tony does those as well. He was the originator of both the motor and hop-up mods.