NOS Aris 12-21 7 spd any good to you? Not cheap at £40 posted but won't let it go for less just in case I need to buy a new one at some point.
Otherwise I have a Shimano 13-18 6 spd you could have for £24 posted.
Also have a little bundle of NOS Aris 8-speed close ratio freewheels. 14-22, 12-21 IIRC