Penny: Hobgoblin have quite a few stores around the UK. Bristol, Leeds, London, Manchester, Nottingham, Birmingham, Crawley and Milton Keynes - So maybe there's one closer to you than Leeds. Looking in their catalogue, they list 21 bar Ashbury ones for £200 and £300 (the second has electrics in it), and it says they're available in all shops (or should be). The chords are apparently Eb,Bb,F,C,G,D,A,F7,C7,G7,D7,A7,E7,B7,Ab, Bb7,Cm,Gm,Dm,Am and Em, which seems reasonable enough.

Eagle Music also have a 21 bar on their website that might be worth a look - I'm a banjo and mandolin player, so I know nothing about autoharps whatsoever, but I've bought a lot of things from that place and can only really say good things about them. They have a physical shop in Huddersfield, too, but if Leeds is far, I imagine Huddersfield would be out of your reach too.