Wheezy does contain that version and has done since 2012-09-05, if you
are using wheezy. If you are using sid, you need to specify the sid
version 4.7.2-4
Yes, I'm on sid, and yes, that's exactly the problem, the 4.7.2-4. libstdc++6-armhf-cross_4.7.2-4_all.deb depends on gcc-4.7-arm-linux-gnueabihf-base=4.7.2-4, which is not installable, as the repository has only 4.7.1-7 (at least for amd64, for i386 it's OK)