I got the print from bumblejax.com, specifically I got their “acrylic proof” product:
https://www.bumblejax.com/prices/
Obligatory warning: Speaking only for myself. Glowforge can’t speak for this supplier.
Relevant anecdote: I bought the print and asked about the plastics used to see if it was laser compatible. They told me that the backing was plastic X, which was not laser compatible. I was suspicious because it didn’t look like plastic X, and asked them to verify. Turns out they’d just switched to plastic Y which was laser compatible, couldn’t be sure if the switch was permanent, etc. Moral of the story: check and double check laser compatibility with your suppliers!