MongoDB 3.0 release for Cent OS
At present ( meaning as of writing ) there really isn't an actual "official release date" for MongoDB 3.0 or is there "really" an official source for the repository of binary builds for any platform.

Results vary for each distribution, but in this case you are probably best following the official documentation links and changing the version in the required "drop-down" to "3.0 (upcoming)" (and again, as of writing). The "repo" location links have been consistently changed over most OS distributions as of the 3.0 pending release. Url's in the documentation likely need "massaging".

Right now the RHEL/CentOS repo for current is here: http://repo.mongodb.org/yum/redhat/7/mongodb-org/testing/x86_64/RPMS/

Following that you can install a "binary build" of the "current release candidate" for your own usage. Failing that then just go for something like: https://fastdl.mongodb.org/linux/mongodb-linux-x86_64-rhel70-3.0.0-rc11.tgz and deploy according to your platform mapping of locations and configurations.

When it's released then it will be released. Contact your local MUG for more info if someone is prepared to give it to you. Otherwise just live with "Soon".