I get them from Amazon. I get this pack and I’ve gotten a 6 pack with a variety of mixed mats (standard, light, string, etc) for $12 or $13 also from Amazon. This is the pack with the standard grip mats

https://www.amazon.com/HTVRONT-Standard-Adhesive-Replacement-Accessories/dp/B08R8GTSX5/ref=mp_s_a_1_5?crid=29B3TOB64O1UG&keywords=cricut+cutting+mats+12x12&qid=1675204225&sprefix=cricut+cutting+mats+12x12%2Caps%2C78&sr=8-5