Yep a damaged bead would be my first port of call too. Also a possibility that your rim might be damaged may not circularly true, i.e. round/has a flat spot
http://sheldonbrown.com/tooltips/truing.html
I am not sure why a good bike shop would not recognise that though ?
If you are happy to build your own wheels (or even get someone to do it for you), Brompton rims are readily available (at least in the UK) and spokes easily supplied cut to size. Saves a fortune rather than buying a whole new wheel and hub.
http://www.sjscycles.co.uk/rims-16-%...9-dept635_pg1/
Regards
Jerry