You can download .gem files using gem fetch:
.gem
gem fetch
gem fetch activesupport consul
Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)
This will produce files like active-support-5.0.0.gem and consul-0.12.1.gem in your working directory.
active-support-5.0.0.gem
consul-0.12.1.gem
Dependencies will not be downloaded.