Yes, there should be a solipsism organization, because it is important to give people an opportunity to exchange ideas. It is kind of a funny concept, because people in a solipsism organization would not be sure that each other existed. However, it is important to discuss this philosophy, as well as to discuss other philosophies.
An organization can exist for Solipsists. It is possibly dangerous, but within a free nation, groups, such as White Supremacists, and Nazis, can have an organization. It should also be the right, as it continues to be, that these organizations can be "frowned upon", but allowed to exist. Well, yes, perhaps we are stuck in the Matrix.