Citing a Work that Cites a Personal Communication
This is a very odd situation, and you may want to consider carefully whether to use the source, per Nate Eldredge's comment above.  If you do want to use it, however, I would recommend citing the textbook, but mentioning their original source in prose:


  blah blah context context, per the table in [citation of Textbook], as attributed to [their source].


This way you give the citation and appropriate credit, but do not assert you have personal communication of your own.