The Luke O'Donovan Support Committee has posted Luke's address (which is temporary and will change multiple times in the next few months).
He can be written or sent postcards at the following address:
Luke Patrick O’Donovan
c/o: Fulton County Jail
901 Rice Street NW
If you've never written a letter to a prisoner, please go here: https://nycabc.wordpress.com/write-a-letter/