It's a rare color-morph of a BTA so all the same care requirements apply. Here's a good source of info for BTA's http://www.karensroseanemones.net/
You may get or lucky or might need to be patient for that perfect nem to come around. Find a couple online vendors with WYSIWYG photos that get them in and watch them closely. Liveaquaria is great but not sure if you'll find a rainbow there. Here's a couple others you can check out: