There's a big hobby mall with lots of numismatic stores, and a big flea market with lots of coin sellers, both within 5 miles of my home (20-30 minutes, with all the public transit). There's one more hobby mall, and a small but popular numismatic-oriented market, within 10 miles (40-50 minutes).
I'm not even counting all the antique shops, the high-end coin shops for tourists, and the random overpriced commemoratives that are sold in every other newspaper kiosk. (Is it still kiosk in English? Oh, whatever.)
I know there's such a thing as online purchase, but I've only ever got one coin online (a few years ago, on a site that doesn't exist anymore). I also got many coins as gifts from CCF members (some, but not all, of these being Secret Santa), and a few from various friends and family who went on vacation to other countries, but for the most part, the coins in my collection come from the places above (okay, a few had been bought at similar places in other cities).