The Lima spares supplier that Hornby recently featured in their news section on their website also does a small range of Bachmann spares. However, my list only covers steam locomotive parts so I don't know if they do DMU spares. You will need to contact M.B Models for an update and they don't have a website. They may know of other Bachmann spares suppliers:-
http://www.hornby.com/pages/nws_det_ann.aspx?NewsItemID=493
Happy modelling
Gary
http://www.hornby.com/pages/nws_det_ann.aspx?NewsItemID=493
Happy modelling
Gary