paperlesspost.com: free save the date options where guests can reply with their mailing addresses! another option can be to send a save the date by email/PDF and then make a google form where guests can fill in their mailing addresses
The Surrounded in Swirls Save the Date Card is modern yet classy! With this trending design, you can change all the colors in order to match your wedding scheme. Personalize the card and see your modifications instantly!