Can I do a state only return for MD?

It depends. You can file your state return only, but you won't be able to e-file it without federal return. You'll need to print it out and mail to your state tax board.  You will still have to complete your federal section, even if you won't file your federal return. 

You can file Maryland state taxes for free on their website regardless of your tax situation as long as your federal tax return has already been completed. (You need the AGI and some other info to complete Maryland.)

In Maryland it's called iFile for Individuals and you can fit it at MarylandTaxes.gov  and follow the menus. (Or directly at https://interactive.marylandtaxes.gov/Individuals/iFile_ChooseForm/default.asp).