Hello Mehdi Sarkeshi,
I would recommend first listing all the available packages on the branch you are using. If possible I would also recommend using one of the latest branches like fido.
Once you have your environment setup please run
$ bitbake -s
This will list all available packages. You may use grep in order to look for keywords, like the plugins available:
$ bitbake -s | grep gst-plugins
And chose from these lists, the packages available should install successfully.