The whole process can take a little time. Best to sign up before you spend money on cards. The cards need to be mailed between 12/1 and 12/7, so there is still time, but folks would need to get on it right away.
2. VoteForward.https://votefwd.org/ With this one, you sign up and print out your own letters, so it is faster than ordering postcards. Again, you provide your own letter sized stamps, they provide the scripts and addresses.
3. Postcards. http://postcardstovoters.org/. You provide postcards, stamps, and message, they provide GA voter addresses.
Time is of the essence. Voting deadlines and the runoff election day are fast approaching:
Nov. 18 - Mail-in ballots start
Dec. 7 - Voter registration deadline for the runoff election
Dec. 14 - Early in-person voting starts