The best time to buy a football jersey is in the off-season (Spring and Summer), but it's always available year round for your convenience.
You can buy jerseys at any sports store like Dicks, any retail store like Target, and especially online.
Advertisements for various sports jerseys are seen almost always during sporting events on television, even at the live event, as well. Social media also plays a big part in advertisement for this product!
You can use a credit card, Applepay, Cashapp, etc. to buy jerseys. Most of the sales are online, nowadays.
I love having a jersey to cheer on my favorite sports teams!