While I don’t personally know of any other organisations that specifically train in document accessibility, I will say this: Document accessibility begins at the source. That is, make your original source document accessible, and the resulting PDF will also (usually) be accessible.
It is a pain in the neck to make already-existing PDF documents accessible. So I would focus on getting Word accessibility right, then all you would need to worry about on the PDF side is general tidying up - running the Acrobat accessibility checker, working with the tag hierarchy and checking reading order.