Hi Darren,
I think your problem is unlikely to be your wheels, but if it is then contact the Thema Dedra Consortium as they have a stack of 14" alloys for Themas.
www.lancia-tdc.co.uk although they will need refurbishment.
I would suspect that the rear suspension crash is the bushes in the trailing (panhard) arms. Usually they go at the front bush and you can detect this by jacking up the car and grabbing the arms. If they are really bad you will be able to wiggle them by hand, but try inserting a large flat headed screwdriver and see how much play you get.
Other bits that might cause the banging would be worn dampers, unlikely if you passed an MoT, OR the bush at the top of the strut.
These bushes are getting hard to find these days so you might need to get Nylatron inserts made.