Where to Actually Find Coins
Coin roll hunting is the beginner's goldmine: banks sell rolled coins at face value, and you search them and return what you don't keep. Half dollar rolls are famous for hiding 40% silver (1965-1970) and occasionally 90% silver (1964 and earlier) coins. Cent rolls turn up wheat cents, and every denomination can hide errors and varieties. Your only cost is time — you spend back the duds at face value.
Check your everyday change and any coin jars in the house. Silver dimes and quarters (1964 and earlier) still surface occasionally, and wheat cents show up all the time. Learn the quick tells: a silver dime or quarter has a solid silver edge with no copper stripe, and pre-1965 dates on dimes, quarters, and halves mean 90% silver.
Inherited accumulations deserve special care. Do not clean anything, do not spend anything, and don't rush to sell. Sort by denomination and date, pull everything pre-1965 and anything gold-colored or odd-looking, and identify things with this app before letting a dealer make an offer. Estate accumulations get skimmed by sharp buyers every day because the family didn't know what they had.
Beyond that: coin shops (great for asking questions and buying cheap starter coins), coin shows (tables of dealers, often with bargain bins), and reputable online sellers. For anything expensive, buy coins certified by PCGS or NGC until your own grading eye develops.