You can’t get a better forage cap today than one of those being made by Conor Timoney.  They are simply the closest reproductions of the originals in every way, bar none.  And the price can’t be beat too.  These caps are copied from an original L. J. and I. Phillips example with a flat brim, perfect for your 1864 impression for Petersburg, and will come with the appropriate corps badge already attached.

L. J. & I. P. Cap - Petersburg