Here are two sites to check out:
http://www.volkszone.com/VZi/ is sort of a British version of theSamba.
Then, there is the UK version of eBay (
http://www.ebay.co.uk/).
The steering box may be different. I saw a rack and pinion on the UK eBay that said it was RHD-specific. I know it's not the same, but the parallel may very well be.
I would also suggest picking up an issue of
VolksWorld. Their advertisers cater to British clients first and foremost. RHD dashes and the like should be available.
I have one word of advice. RHD Beetles and Super Beetles have LHD-configured windshield wipers. This would drive me crazy (although I'm just one zip code away from there anyway).