I did not see the original posting, so this may be redundant.  There are
several organizations for botanic gardens.  In the US, it's the American
Association of Botanical Gardens and Arboreta with a web site at
http://aabga.mobot.org/aabga.  There is also an international
association of botanic gardens but I don't know the contact.  In the UK,
there is the Botanic Gardens Conservation Secretariat, Descanso House,
Royal Botanic Gardens, Kew, Richmond, UK (sorry I don't have the postal
code) which works on botanic garden education issues and plant
conservation.  In the US, there is the Center for Plant Conservation
located at the Missouri Botanical Garden in St. Louis which works with
botanic gardens to conserve plant resources.  Botanists have developed
good search engines on the Internet for the variety of botany resources.
A search for botanic gardens will likely produce contacts for the
organizations I've listed and others.

Hope this helps.
Jane MacKnight