I use the Fedora CentOS 7 test instance as a test environment when trying to track down available packages:
$ sudo yum list swig*
Loaded plugins: fastestmirror
Repository epel is listed more than once in the configuration
Repository epel-testing is listed more than once in the configuration
Loading mirror speeds from cached hostfile
* base:
d36uatko69830t.cloudfront.net * epel:
mirrors.kernel.org * extras:
d36uatko69830t.cloudfront.net * updates:
d36uatko69830t.cloudfront.netAvailable Packages
swig.x86_64 2.0.10-5.el7 base
swig-doc.noarch 2.0.10-5.el7 base
swig3.x86_64 3.0.12-17.el7 extras
swig3-doc.noarch 3.0.12-17.el7 extras
swig3-gdb.x86_64 3.0.12-17.el7 extras