Findmypast.co.uk are apparently going to have historic electoral rolls on their site from 2012 according to a newsletter they recently sent out.
In the meantime apart from libraries \ archives for the area concerned the British Library has teh most complete set of historic electoral rolls.
I don't know how helpful libraries will be doing a lookup for you. When I contacted a library about this last year they would not do a lookup on spec what they would do is confirm a name at an address - fortunately I knew both in that instance