Well, the only rpm repository out there offering subversion above 1.4.x was / is rpmforge (aka DAG).
In order to add rpmforge to your RedHat / CentOs repository one has to update their yum repositories by installing the rpmforge-release package which you can also find @: http://packages.sw.be/rpmforge-release/
The problem I encountered was, I had a Centos 5.5 x86_64 with subversion & mod_dav_svn 1.4.2, after updating to the latest rpmforge-release, I expected a
yum update subversion mod_dav_svn
to do the trick for me well no ...
So after banging my head on my keyboard after trying to manually downloading the rpms (which are there by the way!), and still faling on dependencies.
Reading all I could online in order to solve this issue I stunbledupon: