Answer: Unfortunately in a brief search I am not able to locate a source for this plant. I did notice that the Forestfarm catalog offers several different cultivars along with Vitex rotundifolia which it describes as winter hardy to zone 6.
In your area, I would expect the Vitex in general to be grown as cut back shrubs, meaning they will winter kill severely each year but regrow from the roots and bloom in late summer on the new growth of the season. They will stay smaller with a shrubby form and will not develop into small trees as a result. A sheltered spot with full sun, protection from winter winds and a heavy winter mulch would be helpful in any case.
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