Try something like
idx=find(ismember(enumeration(Example),Example.value999));
A(idx)
SIDEBAR:
MATLAB enumeration classes are weird things -- they are nothing at all like a classical C-like enumeration which is, essentially nothing but a macro #define with scope. In C you get just the constant; in MATLAB you get the whole class thingie as an object that just displays its value and MATLAB functions can get its value, but it's not just the constant. I tried it with constants for an ActiveX class to interact w/ Excel to be able to use named constants in the MATLAB code a la the VBA constants -- crash and burn; MATLAB doesn't send the value but the object.
