The best go-to are these from Amazon; two pack for $15. They're exactly the same quality as all the graphic/printed ones: https://www.amazon.com/Game-Mats-Playmats-Black-Pack/dp/B08974CJHG/ref=sr_1_4?dchild=1&keywords=card+playmat+red+black+two+pack&qid=1628488697&sr=8-4
I just bought these:
Game Mats, TCG Playmats (Black, Red, 24 x 14 in, 2 Pack) https://www.amazon.com/dp/B08974CJHG/ref=cm_sw_r_cp_api_glt_fabc_JYVF28Z4D148GMC31FBC