I now have my plastic parts. I finally went for a set of the cast or moulded parts being sold by fotonlabs on ebay for about £150. I decided it was worth the saving and do the drilling myself (I hope). The seller warned me that they had some breakages reported from the postage, and that they would replace any parts that were broken. They were right, a few parts did arrive broken, but they have been very good and are sending replacements out straight away. The plastic is quite brittle, and the seller has told me they are changing the plastic mix to be more flexible. I have had a go at drilling a few parts, and the seem to drill pretty well but I think as the plastic is quite brittle I will have to take care and not rush it.
I will be moving to a new house and job in a month, this might get in the way of making quick progress but I should still find an hour or two here and there.