Some time ago I've read somewhere (on this forum?) that Active Directory contents can be published via a web service. So you might be able to invoke a web service using a Web Service Consumer transformation.
Just an idea.
For a possible workaround:
We used to export AD data through Powershell and add them to a sql db, this sql database was used in powercenter. In our case it was only samaccountname and personal number.. But the properties can be expanded.
IIRC, github has a few samples to export ad data to sql database
Hope it helps