John : First, are you looking for NOS, or just an excellent, functioning used one ? Or either ?
Being a "one year wonder", either of course will be a challenge. The one "saving grace" might be the fact that as well as being used on 289 Mustangs with both 2v and 4v carb engines with both T/E and A/C, it was also used on 1967 Fairlanes and Falcons with the same components.
Also of note is that sometime between May of 1975 and July of 1976, the C70Z-12A091-A was replaced by the C70Z-12A091-C ; however, this was very short-lived as by July 1976, both Part Numbers are shown as "NR" (Obsolete).
Bob