Counting Multiple Occurrences of Text in a Cell

With
A1: containing text.....e.g. AbcdefgAhijklmAnopqrstAuvwxyAz
B1: a character to find...e.g. A

This regular formula returns the position of the last occurrence of that character

 
C1: =FIND("|",SUBSTITUTE(A1,"A","|",LEN(A1)-LEN(SUBSTITUTE(A1,"A",""))))

In the above example, the formula returns: 29

Note: That formula is case-sensitive...so if A1 contains lower case a's, they would be ignored.
If you need it to NOT be case-sensitive...try this:

C1: =FIND("|",SUBSTITUTE(UPPER(A1),B1,"|",LEN(A1)-LEN(SUBSTITUTE(A1,"A",""))))

Is that something you can work with?