I recently finished reading Tim Smith's book "The Union Assaults at Vicksburg" and he has an extensive bibliography. I will toss out a few that I see and page number listed in bibliography.
Letters & Journals at Vicksburg NPS.
John O'Dea, " A forlorn Hope" -- pg 453
. . . Original in Chicago Times Herald, May 30, 1897 and reprinted in John O'Dea, "A Forlonrn Hope", in Transactions of the McLean County Historical Society, Vol 1 (Bloomington IL: McLean County Historical Society, 1899), 477-480.
J. B. Allen Letter, 30th Ohio File -- 452
Robert McRory Letter, 30th Ohio-- pg 453
W. Schalenburg Letter, 37 Ohio File -- pg 453
Thomas J. Taylor Letter, 47th Ohio File -- pg 454
More references from Footnotes:
#48
September 29, 1910, National Tribune.
Brinkerhoff, History of the Thirtieth Regiment Ohio Volunteer Infantry, 72-73, VNPS
History of the 37th Regiment, O.V.V.I., 21-22
#49
J. B. Allen to W. T. Rigby, July 12, 1904. 30th Ohio File-- VNPS
Robert McRory to J. B. Allen, APril 15, 1904, 30th Ohio File-- VNPS
Isaac T. WIlliams to brother June 18, 1863, Isaac T. Williams Papers, Tim Brookes Collection USAHEC.
#50
W. Schalenburg to W. T. Rigby, March 12, 1901, 37th Ohio File-- VNPS
#51
Henry Schmidt to wife, May 24, 1863, Schmidt Family Papers, Filson Historical Society, Louisville, Kentucky.
#56
Saunier, A History of the Forty-seventh Regiment Ohio Veteran Volunteer Infantry, 147-148
#58
Clarke, Reminiscence and Anecdotes (accounts of a member of 36 Mississippi Regiment)
That is just a few that I could match up with first hand accounts of regiments in the Forlorn Hope. There are probably other accounts from the Confederate side. I recommend you borrow or buy Tim Smith's book.