I've been looking but without great success. I see that electricwheel.co.uk do a 80mm Nano kit for the Brompton which they will supply for other makes. I'm not sure whether they would charge £650 or £750 for one fitted in a 20in wheel. There have been comments on the forum about slow delivery and difficulty in contacting them, but they did reply very quickly to my email about delivery charges. For the moment I've decided to keep my Dahon unassisted and perhaps put the money towards a new full sized electric bike so I didn't take it any further.