Souvenir shops will sell you a shot glass you'll never use. The patch rack is usually in the back. Head there.
National park visitor centers. The gold standard. Nearly every park, monument, and national forest sells an embroidered patch, usually under $6, usually designed decades ago and better for it. Ranger stations at the smaller sites often carry versions the main gift shops don't.
State parks and roadside attractions. Inconsistent - which is the point. The state park patch you find in a drawer under the register is the one nobody else's jacket has.
Thrift stores and antique malls. Look for the jar of loose patches near the register, and check old scout uniforms and work shirts on the racks. Vintage patches carry someone else's miles before yours. We consider that a feature.
Diners, dive bars, trading posts. If a place has a logo and a sense of humor, ask. Half the time there's a box of patches from 1987 in the office.
Gas stations on old routes. Route 66, Highway 1, the Blue Ridge Parkway. Tourist corridors keep the patch tradition alive better than cities do.
What to skip. Airport gift shops. Anything holographic. Patches for places you didn't actually go - the jacket keeps an honest record or it keeps nothing.
Carrying them home. A patch weighs nothing. Buy the patch, write the date on the back in ballpoint, and sew it on when you get home - or in the motel that night if the trip earned it. (Our guide to sewing them on is here.)
The Rambler was built for exactly this - a work jacket that starts with your home state and fills in with everywhere else. Every patch writes the next chapter.