Well this isn't keyed or a wheelchair wheel lol... but may be useable???

http://www.rosscastors.co.uk/330mm-h...ic-centre.html


not sure what size these are

http://compare.ebay.co.uk/like/13090...ff14=64&ff19=0


may be useable?
http://www.ebay.co.uk/itm/2-invacare...item20d17d522b

http://www.ebay.co.uk/itm/spare-part...item27d223e935