Part of the TAM Rubberstamp Archive still in New York; I want it back.

Greetings from Dadaland was an exhibition at the Stendhal Gallery in April-May 2010. I sent in a selection from the TAM Rubberstamp Archive and went over myself doing a lecture explaining my views of the network. One year later I am confronted with a real problem connected to this exhibition. Harry Stendhall, the Gallery owner of Stendhal Gallery , has yet to return the 670 stampsheets he has in New York. I have asked him often, also asked John Held as a currator to help me on this but the sheets are still not here. I have set a deadline twice (Januari 2011, and now June 1st 2011) for him to return my belongings, but he allways promisses that he will do so, but actually doesn't. So with the second deadline I have told him I will go public with this problem, and will seek help in this. Probably also my lawyer in forcing the return of this specific part of the TAM Rubberstamp Archive. It seems that mail-art and the official art-world don't always fit well together. The collection that Harry Stendhal has is essential to my basic collection I have here in Breda. It needs to be returned. Any advice in how to deal with this situation is welcome.