I'm not sure is the honest answer, I'm near Dorchester and know of a couple of Garden Centres that aspire to be like the stores you mention.
I wonder if anyone else might know?
Its pretty quiet on here at the moment, but as Dorset Editor (started on Monday 17th February) i'm doing lots of research to see what is about in Dorset.
If you find anything yourself please let me know, in the meantime the one place I have visited which might go some way to meet your needs is