I bought mine on Amazon! Here’s the exact model: Ergon Games - Parchment 2 ft x 3 ft DND Mat, DND Battle Mat, Battle Grid Game Mat, D&D Map, D&D Mat, Battle Map, D&D Battle Mat, DND Battle Map https://www.amazon.com/dp/B07K4KKWJJ/ref=cm_sw_r_cp_api_glt_fabc_PQ4WD5YAJQASD8KAAHSS?_encoding=UTF8&psc=1
It’s not cheap, but I find it so worth it. Lays flat every time! It even folds super well if you need less space than the entire sheet spread out.
The only negative I saw in the reviews was that red marker tends to stain if you leave it on too long. I bought the Bic Intensity wet erase markers advertised on Amazon along with this mat and didn’t have issues using the red since I cleaned the mat off afterwards.
I personally drew a massive sword coast hex map over the entire hex side and left the wet erase marker on for over 2 months! No staining when I cleaned it off, but I also didn’t use red purposely.