David:
Where are you located? (Please update your profile to include your two-letter country code to make it easier for us to find out - helpful when answering questions.)
Tonka beans (and extracts) are not allowed as a food ingredient in the US since 1954 because they contain coumarin.
There are many other common foods that contain coumarin whose consumption is not prohibited, but if you were to list tonka beans as an ingredient you would be breaking the law.
That said, they appear to be easily available on Amazon.
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@DiscoverChoc