Short version:

I would very much like a scan of the original letter mentioned below. But have not been able to find it online myself. Alternatively a picture of the letter in a book.

Long version:

I have found this letter referenced several times, among others by u/Bernardito of this channel.

https://www.reddit.com/r/AskHistorians/comments/28geqi/did_himmler_actually_search_for_atlantis/

Himmler himself requested a search for evidence of Thor's hammer to the Ahnenerbe in a letter from May 1940:

Have the following researched: Find all places in the northern Germanic Aryan cultural world where an understanding of the lightning bolt, the thunderbolt, Thor's hammer, or the flying or thrown hammer exists, in addition to all the sculptures of the god depicted with a small hand axe emitting lightning. Please collect all of the pictorial, sculptural, written and mythological evidence of this. I am convinced that this is not based on natural thunder and lightning, but rather that it is an early, highly developed form of war weapon of our forefathers, which was only, of course, possessed by the Aesir, the gods, and that it implies an unheard of knowledge of electricity.

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I did not find it in The Master Plan, when I had the opportunity to check it. But I might have missed it. I have not yet had the opportunity to check Heinrich Himmler: A Life. And again, I would prefer a copy of the original letter, but a reference would be better than nothing.

Any help/info you can give will be much appreciated :)