Question: Are there any half-official repositories for CentOS 5 with Python 2.7?

EPEL provides only Python 2.6

Answer: 
Have you checked any of these repos:

* [Dag Wieers](http://dag.wieers.com/rpm/)
* [Dries](http://dries.ulyssis.org/rpm/)
* [rpmforge](http://rpmrepo.org/RPMforge)
* [livna](http://rpm.livna.org/)

Is it ok if you have the rpm instead of a repo (i.e. can you take care of dependencies if it arises?). If so, try [phone](http://rpm.pbone.net) or [rpmfind](http://rpmfind.net). If none of the above helps, consider building from source tar balls. By far that will be the easiest.
You can try to get 2.6 srpm from epel you've found, extract spec file from it, change version number and rebuild it.

However, be carefull: there are a lot of packages depending on python 2.4 on el5 (like yum). You'll probably need to ensure that you are installing 2.4 and 2.7 at the same time or that you've rebuild everything depending on 2.4.