Sadly, there just aren't enough people playing the game in online multiplayer to support having mods or custom maps.  (What I mean is that if 5% of the people who play the game online would be sophisticated enough to know how to add custom maps and mods and willing to take the time needed to do it, there just aren't enough total players online so that the 5% is a large enough aggregate number.  In contrast, if 3000 people were online at once, which is what this game deserves, then you would be able to find any type of game you want to play.)

I think your best bet would be to try to arrange a game with people and schedule a time to play the mod you want to play.  Best bet might be the "Multiplayer" forum instead of "Multiplayer Organizer".  Also, include links to where people can download the mods and tell us whether the game and the mods are for regular Sins or Entrenchment.

I play in a group sometimes twice a week. We have a custom mod we use that we play custom maps.. If you want to join our group let me know. We play usually Saturday nights at 7:30 PST using direct IP.

-Aaron

We play our modified version of SINSPLUS for Entrenchment. You just add it to your mod folder and enable it. Our mod has no effects or changes to the game files, since I keep it up to date with the latest versions. If you are  still interested, PM with your e-mail and I will add you to our e-mail lists and give you the link to DL the mod.

-Aaron