There is a plant fair at Sturminster Newton this weekend, to be held between 10-4 in the Railway Garden on Saturday 2nd June.
http://www.rotary-ribi.org/clubs/page.php?PgID=689612&ClubID=683
On Sunday 3rd June, it’s the Solent Gardeners Fair held at the University of Southampton’s sports ground between 10-4. This is a very large event and well worth going to.