Where to go get a spare car key?

I bought a used car from a family friend and everything is fine with it. However he bought the car new back in 2011 and has since lost the spare key. I have stopped myself from locking my keys in the car a few times now and think it’s best I get a spare. I know I can order the fob off of Amazon or from a store like advanced auto parts but the car uses an actual key. Can I go to any locksmith or do I have to go to the dealer for that?