This particular repository has GD::Graph and other associated GD modules:
http://theoryx5.uwinnipeg.ca/ppms/
You can add it to the repositories that the ActiveState PPM accesses by issuing the following command at the PPM prompt:
ppm rep add theoryx5.8ca http://theoryx5.uwinnipeg.ca/ppms/
I have found this particular repository to be very useful. It contains a lot of the modules for the Active State Win32 Perl Installation that the Active State Repository doesnot contain for one reason or another.