The RHS site (Royal Horticultural Society) is a good place to look. Click on their 'plant finder' and it will give you local suppliers and mail order suppliers. Hope this will help.

Loder Plants near Horsham have a vast range of Rhodies.

Thanks guys. I have actually tried both of these without success. Also Burncoose nurseries used to stock but say no longer available.
John

I suspect it would be wise to leave out planting large rhododendrons - the Cornish Red variety is a cross with R. ponticum, and phytophthera kernoviae and p. ramorum use R. ponticum varieties in particular as a host plant, but also infect any and all rhododendrons. Cornwall has a significant problem with both forms of phytophthera, and R. ponticum plants in the wild were being removed to try to limit the spread of these fungal infections. This may be why you're finding it difficult to source the plant.

Wow . . . well, you can always trust Bamboo!

Hmm, Sheilabub, not sure what that means - maybe 'you can always trust Bamboo to present the down side' lol!

:)) Your detailed horticultural knowledge is so impressive, Bamboo. Is it your day job?

Yes, Sheila, though I'm semi retired from actual physical gardening these days.