The upstream used naming for python-config is 'pythonX.Y-config'. Please fix your package to use that rather than relying on Gentoo-specific 'python-config-X.Y'. This can be often fixed by removing some patch, sed or configure override.
-9999 fixed.
A modern note: if you're using python-r1, python-single-r1 or python-any-r1, it's not necessary to use 'python-config-X.Y' or 'pythonX.Y-config' anymore. The eclass puts a local symlink to proper 'python-config' variant in $PATH, so the build system can just take 'python-config' and it will get the version desired. If the build system in question respects PYTHON and looks for appropriate pythonX.Y-config itself, great! If it doesn't, there's no need to hack it in. Just let it use python-config and the eclass will do the rest.
Oh, and the releases having it are obviously long gone ;).