For hockey cards, my understanding is Upper Deck often buys their game-worn jerseys directly from teams or they go through reputable companies like MeiGray or Classic Auctions. Players now go through a lot more jerseys than they used to, so current ones are much easier to acquire. Some players now wear a new jersey almost every game. Many retired players may have only worn a handful per season, and those are much tougher to acquire.
Once a card company has a jersey, they can make it last a few years. If it’s a jersey of a star player from the 90s or older, they will make the jersey last for many years by limiting how often it is used and the size of the pieces used for hockey cards. The main set where Upper Deck would prioritize those older jerseys is for their highest-end product called The Cup, which is the set where those Fuhr patches were used in the picture I posted.
Another thing that has been happening for about 20 years, is the language of the backs of hockey cards has changed. They used to commonly say the memorabilia on the front was “game-worn”, but now most cards say something like the memorabilia was “player worn” or “event used”. This means the memorabilia wasn’t necessarily game-worn. This is very common with rookies, which Upper Deck has a heavy presence at the NHL Draft and Rookie Showcase. Upper Deck could hand a player a jersey to wear while they sign autographs for the company, and now Upper Deck now has a player-worn jersey for hockey cards immediately. My understanding is they do similar things at the All-Star Game and Winter Classic, and another other events with current and retired players as well. This increases availability of jerseys to use and reduces cost since they aren’t game-worn.