gtk2-2.24.30 and all its dependencies are available on AIX toolbox.

https://public.dhe.ibm.com/aix/freeSoftware/aixtoolbox/RPMS/ppc/gtk2/

Following is the list of packages and dependencies those are added/updated for gtk2-2.24.30 on AIX toolbox.

atk-2.20.0-2.aix6.1.ppc.rpm
cairo-1.14.6-1wofX11.aix6.1.ppc.rpm
fontconfig-2.11.95-2.aix6.1.ppc.rpm
freetype2-2.6.3-1.aix6.1.ppc.rpm
freetype2-demos-2.6.3-1.aix6.1.ppc.rpm
gdk-pixbuf-2.35.1-1wofX11.aix6.1.ppc.rpm
gtk2-2.24.30-1wofX11.aix6.1.ppc.rpm
gtk2-immodule-xim-2.24.30-1wofX11.aix6.1.ppc.rpm
gtk2-immodules-2.24.30-1wofX11.aix6.1.ppc.rpm
harfbuzz-1.2.7-1.aix6.1.ppc.rpm
intltool-0.51.0-1.aix6.1.noarch.rpm
libX11-1.6.3-1.aix6.1.ppc.rpm
libXau-1.0.8-1.aix6.1.ppc.rpm
libXdmcp-1.1.2-1.aix6.1.ppc.rpm
libXft-2.3.2-2wofX11.aix6.1.ppc.rpm
libXrandr-1.4.2-1wofX11.aix6.1.ppc.rpm
libXrender-0.9.9-1.aix6.1.ppc.rpm
libpng-1.6.21-1.aix6.1.ppc.rpm
libpthread-stubs-0.3-2.aix6.1.ppc.rpm
libxcb-1.12-1waixX11.aix6.1.ppc.rpm
libxcb-1.12-1wofX11.aix6.1.ppc.rpm
pango-1.40.1-1wofX11.aix6.1.ppc.rpm
pixman-0.34.0-1.aix6.1.ppc.rpm
renderproto-0.11.1-1.aix6.1.ppc.rpm
shared-mime-info-1.6-1.aix6.1.ppc.rpm
xcb-proto-1.12-1.aix6.1.ppc.rpm

You can also use YUM to install/update gtk2.

Thanks

Sanket