Had some books go lost.  PM'd people with a nice message whether to hold out longer or reorder blahblah.  Had one respond saying still had books would mail next day priority mail if I still wanted them.  I said I would still love to receive them.  Its been 7days.  There are only 3 other copies in the system would you reorder from someone else or wait longer?

You should notify the PBS site administrators about the swapper that marked them as Mailed, and yet still had them on hand after the 26-day period when they went "Lost" in the system.  Especially since they'd send them out Next Day Priority for you and it's been a week.

I'd reorder from someone else, myself.  Your Sender has shown themself to be untrustworthy about mailing their books.  And if I received a duplicate copy, I could always repost it here for someone else to order, it shouldn't be too long a wait for a request if there are only three other copies in the system.

If the system has declared the books lost and you've gotten the credit back, then I would reorder. It sounds like the first sender isn't very reliable. It takes a month for a book to go "lost" and the sender apparently couldn't manage to mail it within that time frame.

Where do I go to make a report of the problem. 

Go to the bottom right hand side of any page and click on CONTACT US. Send a feedback about the situation making sure to include the person's username and the book(s) in question.

Corner of any page.  At the bottom, under Company is Contact Us.  (Live Help gets you a volunteer tour guide.  Contact us is the Admin.)

I would cover my bases with the original sender before re-ordering since you told her/him you still wanted them. Send her/him a PM stating that if the books do not arrive by X date, you will be reordering the books and she/he will not get credit from you. That way she/he doesn't mail them and claim you said you still wanted them.

Since you responded to the original sender that yes, you DID still want the book, you will be obligated to mark it received when it comes.    So like Melanie said, I would make sure that the original sender hasn't sent the book yet.    If not, then tell her not to send it so it's on the record that you did that.   If she has sent it, then I would wait at least another week.