Hot topic/box lunch and others carry bags that have a display spot in the front. Gopinpro (on Instagram) has some cool ones as well. On eBay you can find used legit ones or cheaper knockoffs. They sell them at the parks, too. Personally, I use those large fabric-covered 3 ring binders with a zippered cover and strap (amazon or staples) and use trading card plastic inserts to keep the pins/cards in place and on display. Happy trading!

Edit: Amazon Basics 3-Ring Binder with Zipper - O-Ring, 3 Inch, Black https://www.amazon.com/dp/B07D8R4872/ref=cm_sw_r_cp_api_glt_fabc_T5MSKRHNN50BKWRR0AA6