I dont think you need loweq for this-they will bring no vlaue to the process-and charge a fortune for it. Do it your self.
I too only got a receipt for the amount the builder charged to the flipper. The rest-which as you say, make the full purchase price, has not been receipted to me and may take a while to get.
Anyway Revenue wont give you a refund on the full price paid unless the extra amount of VAT has been receipted by them. The residency of the flipper is irrelevant here as the goods have not been exported. There is no such thing as a duty free exemption on property sales.
Best thing is to get receipt in your name from the builder, make VAT return and supply cover letter stating you paid more and cannot get a receipt. Give details of the flipper and ask them (through your solicitor) to investigate VAT avoidance. See other post on 'selling on Contract'