We live on the Shropshire/Cheshire border and we have Bridgemere garden
world just up the road from us. It is massive and we bought 4
Rhodedendrons from them last week. They claim to have the largest
selection of plants in the UK and you need at least a day to wander
around it because a couple of hours is never enough! You can go online
and check if they have what you want as well. Just Google - Bridgemere
Garden World. I think it is infact within the boundaries of Shropshire
(just) and may even be not too far from you.

Hope this helps and good luck with your search.

Gail