Sue, your suggestion re placing addresses in the "Profile" section appears to me to be the most logical and un-complicated method. All present members who do not already show their address should update their profile to include this, and new members should be directed to do so when registering.
If anyone is hesitant about posting their address on the site, perhaps Admin could set something up which would require permission to allow access or not. This of course would not solve the problem of contacting the authors of old messages but would help in the future.