I got it off Amazon, but it’s a little pricey, you can also find them off Aliexpress. The one I have above is actually for a full size keyboard I was using before, but since I switch to the TKL now, I didn’t feel like buying another one just for it. So the full size will fit tkl or smaller boards along with a mouse.

MagiDeal Transparent Sturdy Acrylic Guard Anti Dust Keyboard Cover Minimalism Easy to Clean for Keyboard Desktop Culture & No Pads - Type B, 375x150x48 mm 14.76x5.91x1.89 inch https://www.amazon.com/dp/B08ZM696HX/ref=cm_sw_r_cp_api_glt_i_D2813V5A257XZRCQ3SA3