Where can I get signed items by Vivekananda, Tagore,Gandhi?

I was born in India but moved to the UK when I was 2. I presently live in Japan.I collect old mcripts, letters, signatures.I'm looking to buy letters doents signed by Gandhi-Mahatama or Indira,Nehru, Vivekananda,Mother Theresa. Top prices are paid for genuine interesting items. I hope someone can help me.