donor of artificial insemination

Usually you can try to go back to the clinic that it was done at. If that donor has allowed the clinic to give his information out they will tell you. If the donor wishes to remain nameless then they have to honor his wishes.

i have no idea.

If you know what clinic was used you may be able to get the information from them.

Yes, there is an organization to find siblings and perhaps donors of artificial insemination. A few months ago I read an article about such an organization. I cannot recall the name, but I'm confident that if you conduct an online search using "artificial+insemination+siblings+organization" (without the quotation marks), you will find what you seek.