Hi if look here http://www.rctank.jp/machine/tiger-e.htm, this is the 'extra channel feature' i wanted,
and if you look here http://www.rctank.jp/machine/tiger-e.htm this is who makes them.

I can't take credit for finding these people, as there URL came up on the 'who sell what' link before mr.moderator tokk it away!

Yours Simon M.