As Neil already said, it shouldn't be a problem ordering a RHD car from any dealer.
Your best bet, though, would be to order it in a high VAT country, like Denmark, and then import it into Germany
before taking it to the UK. Especially as getting the car from the border is easier here than in the UK, as you just need to get a "5 Tage Kennzeichen" to get it here.
The manufacturers adjust the net price, before VAT, to equalise the final sales price, so that there is less difference in the gross prices between the countries. If you then import it into Germany, you only have to pay 16% VAT on the lower net price instead of the 17,5% which you have to pay C&E for a "NMT" (New Means of Transport).
If you have payed the VAT in one EU country, you don't have to pay it in another. Getting a car that you own, and is registered in Germany, re-registered for private use in the UK is a formality.
If you are going to export it, you can also get an "Ausführkennzeichen", which is valid for 6 months. Both of this and the "5 Tage Kz" allow you to drive across borders, so getting to the UK is also not an issue -- (DVLC recommend transport for unregistered new cars - see link below) -- and you can drive around during the 14 days to a month it takes for the formalities in the UK.
No matter what, if you have owned the car for more than 6 months, it counts as a used car, and you don't have to pay any tax when you import it privately to the UK. You just have to drive it there, get it cleared by customs, insured and register it with the
DVLC.
If you are planning in advance, order your car with a delivery date at least 6 months before you go back to the UK. If you're feeling shy about doing the import to DE yourself, there are enough importers here. Even some franchised dealers do EU imports.