Yes, you can buy additional states from within the program, as long as you have a US credit or debit card with a US billing address.
You have to start a 2017 tax file before you buy any state
Start your Federal entries first. then work on your Free state and select it as your free one when you start it.
.....then, after that, when you start on the second state, you will be asked to pay $40 (ok..39.99 for the nit-pickers).
(Maine isn't available yet)
When you buy your Deluxe in a store, read the box carefully, since Deluxe comes in 2 versions--one that is Federal-only, and one that is combo Federal and State.