Invite friends, neighbors, coworkers, or make arrangements with a club you are a member of. You can host at your home, at a coffee shop, a restaurant during happy hour, or at any other community gathering place. Print out post cards on heavy-duty cardstock and cut them out.
Or have people make their own cards out of sturdy 4X6 index cards. Collect donations for postage and send them to each of your Congressional representatives.
See the Save Santa Ana postcard as an example