Tracking down dahlias

I'm trying to track down these dahlia tubers but can't find hide nor hair of them to buy in the UK. Does anyone have any ideas? I'd be interested in similar ones of height and colour - ie dark red to purple, as tall as I can get. Thanks
D. Admiral Rawlings
D. coccinea Mary Keen
D. coccinea Great Dixter
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It gets to about 5ft and the flowers look like those above, a really deep red.
But I have found that for the last few years the colour is now quite a bright red and the flowers are now only semi-double...
Do the tubers change somehow over the years?
Wisdom is not putting it in a fruit salad.
https://www.farmergracy.co.uk/products/dahlia-thomas-a-edison-tubers-uk
My favourite at the moment is Dahlia Lou Farman - big single flowers that start off intense deep raspberry red, but then the outer petals soften in tone as the flowers age leaving a red ring in the centre. What I like most is how they are held aloft above the foliage on dark stems, it gives a very airy look.