Higgs paper ``A category approach to Boolean valued set theory'' As Philip Scott says
about Denis Higgs:
In category theory, he wrote an influential and beautiful long paper, "A
category approach to Boolean valued set theory", which initiated many
early students in topos theory in the 1970s to Omega-valued sets.
I wonder to know if there is a way to get access to the following paper by  Higgs:

``A category approach to Boolean valued set theory''

Remarks. I am aware of some similar works, for example A category-theoretic approach to boolean-valued models of set theory or the book Sheaves in geometry and logic by Mac Lane and Moerdijk.
 A: Definitely not a answer, but too long for a comment, and just for completeness:
As pointed out by მამუკა ჯიბლაძე, Higgs writes in Injectivity in the Topos of Complete Heyting Algebra Valued Sets that this paper is related to the unpublished paper you are looking for (cited as [5] by Higgs):

An earlier version ( [5] ) of this paper was accepted for publication in
  the Canadian Mathematical Bulletin but for various reasons I discontinued the process of seeing it through into print. In addition to the present
  contents, [5] contained: a brief account of logic in $\mathcal L(\mathcal A)$; the Lawvere Tierney version (for $\mathcal L(\mathcal A)$) of the independence of the continuum
  hypothesis [14]; a sketch of a proof that $\mathcal L(\mathcal A)$ is equivalent to the category
  of sets within the universe $V^{\mathcal A}$ of $\mathcal A$-valued set theory; a mention of
  sheaves on an arbitrary site from the point of view of $\mathcal A$-valued sets; and
  some elementary remarks on boolean powers and ultrapowers in relation
  to $\mathcal L(\mathcal A)$.

[5] D. Higgs A category approach to boolean valued set theory, preprint, University of Waterloo
(1973)
[14] M. Tierney, Sheaf theory and the continuum hypothesis, in Toposes, algebraic geometry and
logic (F. W. Lawvere, éd.), 13-42, Lecture Notes in Mathematics 274 (SpringerVerlag, Berlin, Heidelberg, New York, 1972). 
