Christine,
I dont know of a way to return the Quarter in a Custom Format, or any other.
However, there is a formula to use to do this yourself:
=IF(MONTH(A1)<10,IF(MONTH(A1)<7,IF(MONTH(A1)<4,TEXT(A1,"yy")&"Q1",TEXT(A1,"yy")&"Q2"),TEXT(A1,"yy")&"Q3"),TEXT(A1,"yy")&"Q4")