Answer: As I read your question, I though, I'll never find this! But here's a possibility. I'll quote right out of the Audubon Society's Field Guide to North American Trees:
Clammy Locust (Robinia viscosa): "A small tree with a spreading crown...often spiny, with showy pink flowers and sticky or clammy gland-hairs on twigs, leaf stalks, flower stalks, and pods." Individual flowers are about 3/4" long, shaped like pea flowers, and hang in drooping clusters. The tree produces 2-3" sticky pods, whcih contain the seeds. The range of this tree is from West Virginia southwest to central Alabama, but has become naturalized in other areas.
Now, where to find one! I looked for quite a while, but didn't find any sources. However, both the Arnold Arboretum and the Brooklyn Botanic Garden list the tree. And Twombly Nursery lists lots of rare plants:
Arnold Arboretum: http://www.arboretum.harvard.edu/main.htm
Brooklyn Botanic Garden: http://www.bbg.org/nymf/encyclopedia/fab/rob0030.htm
Twombly Nursery: http://www.twomblynursery.com/plantsninetyeight.htm
This should at least give you some leads!
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