any good locksmith shop should be able to make you a key from your OEM unit. When I got my 79, it cost $2 per key, and took about 5 minutes. Local hardware stores may be able to do them, but if not, find a locksmith shop.
To answer the second part, yes they can cut a new key given your OEM code on your key. It'll be easier if they just copy what you have now.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.