I believe that Credit Suisse no longer does this. They did it for me once, and it took several weeks. I signed the form in the presence of my CS adviser, he sent it to CS Boston with his testament as to who I was, they sent it back with the guarantee finally. I was then told that it could not be done again in the future. Wouldn't hurt to ask though.
Last year, I went through an extensive interview by phone with Vanguard, my custodian, and they did not require a guarantee. They asked questions about things which I had no idea that they knew.
Dredging this up again because a friend here in Switzerland, who wants to gift shares from a US account to his child in the US, has been told he needs to get a Medallion Signature Guarantee to make this happen. As of 2012 it appeared this was not available in Switzerland (or perhaps all of Europe). Has anyone found an answer over the intervening 6.5 years since the OP? Many thanks.