I don't think there is an actual site that has pictures of each variant. The only place that I think has something like that is the Aqualog book. And since I don't own one I could not even say if it actually has each variant. I believe Taz, Scat or Salty1 own one.
There are several pics of some really nice marmoratas on Oliver's site, www.BelowWater.com. A couple of these pics are from there and others from random places I've found. Trombetas, Tapajos, and Orinoco is what they were labeled, check the pic name for the collection location. I would love to have a nice trombetas or orinoco marm ~Trent