Sorry, but I don't really have the time to install LibreOffice and make sure the Mail Merge still works. Although I believe LibreOffice can open Office documents. It might need some massaging after you open it in LibreOffice or OpenOffice.
I have to assume they have a good reason for the delay. My cards are on back-order as well but they haven't charged me yet so no harm or foul. I am sure some will be available before Christmas. Plus, if they wait too long someone will just type them up on MSE and then they will be cheap to print yourself.
I was charged for the first three spell decks today and received an invoice (October 14th). I also received separately an UPS shipping notice. I believe that my spell decks are on the way.