FBI in swansea seem to have a good supply of rust free stock, but you do pay a premium as it's their business. otherwise, something like this
http://www.ebay.co.uk/itm/VW-BAYWINDOW-TYPE-2-T2-CAMPER-BUS-RIGHT-HAND-DRIVE-BEAM-AXLE-SOLID-RUSTFREE-/230728479176?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item35b87d31c8#ht_500wt_1202" onclick="window.open(this.href);return false;
would be fine, but you can get second hand parts cheaper than that, and you'd need a courier, obviously.
anything from august 1969 will fit, but you may have to put the servo bracket from yours on there if you have one.