It was an initial thought that “Blackstone Publishers” might have been a name DeC used to release his own “DeCasseres Books“, though I have stumbled across a few other titles attributed to them from the same period NOT by or about DeCasseres:

The Washington Nursery  by Katharine Emerson Hovey Seabury, 1936

Yerusholayim Shel Matah by Uri Tzvi Greenberg / Cowen, Charles A. (trans.), 1939

Orthod Oxen of Science by George F. Gillette, 1936

It’s possible DeC published these titles under his own imprint. Two of the titles are poetry, one is crazy cosmic pontification.

Details from various web sources on each title:

The Washington nursery
Author: Katharine Emerson Hovey Seabury
Publisher: New York : Blackstone Publishers, ©1936.
Genre/Form: Satires / Anecdotes
Document Type: Book
Fly title: a short history for babies–just babies.
Issued in illustrated & printed buff wrappers.
Description: 16 pages ; 17 cm
Other Titles: Short history for babies
Responsibility: by K.E.S.

Jerusalem: Yerusholayim Shel Matah
Rinberg, Uri Tzvi
Trasnslation from the hebrew by:
Cowen, Charles A.
Blackstone Publishers
New York 1939
8°. 43 p.

This is a different listing of the above,

GREENBERG, URI ZVI & CHARLES A. COWEN (transl. and introd.). – Jerusalem. Yerushalayim Shel Matah.
New York, Blackstone Publishers, 1939. Orig. gold-printed stiff black wraps. with stapled blue cloth spine; rusty staples, top of spine worn and with small library label. 46 pp.; some annotations in pencil in margin. EUR 20.–
~First American edition. Eight poems by Greenberg, introduced by Cowen.

Orthod Oxen of Science: Synoptic conspectus of author’s Unitary Theory.
Published by George F. Gillette,
Author of Unity of Universe, Cycle of Power, Rational Non-Mystical Cosmos
at the Blackstone Publishers
New York City, 1936.
(more on this one here: http://www.logiston.com/oddends/2007/05/the-mystic-mistooks-witch-doctors-of-science/ )

Orthod Oxen of Science was referenced in Donna Kossy’s book KOOKS, by Feral House… here is an excerpt:

Here is a current image of 117 West 27th St., New York, the address listed for Blackstone Publishers in the DeCasseres Books:

While I’m here, I stumbled across this item:
http://www.angelfire.com/nb/shestov/fon/fondane_full.html

Conversations with Lev Shestov
by Benjamin Fondane

February 17, 1937

– You remember Casseres (the American writer). I told you once that he had published a book on four or five big names: Buddha, Spinoza, Nietzsche, Jules de Gaultier. I can’t remember who was the fifth there. J. de Gaultier probably sent him my “The Good in the teaching of Tolstoy and Nietzsche”, judging from the foreword he wrote. I suppose this is how Casseres discovered my books. He just published an article about me, “Samson in the Temple of Fatality” [*]. Seeing the title, I thought he understood what it was all about. But from what I could decipher (it’s in English), he begins with a discussion of my style; I immediately saw that it was not going to be good. I remember a philosopher who once wrote to me that my style is so impressive that it makes one forget all the rest.

[Benjamin De Casseres, “Chestov: Samson in the Temple of Fatality”, chapter 3 of the book “Raiders of the Absolute”, New York, The Blackstone Publishers, 1937, 56 p]