Unable to install logstash-devutils locally for offline-packaging

I am trying build a dev-env for my work-stations where i do not have access to the internet. I was hoping to install basic gem offline and transport it over to my work-station however while trying the below command:

gem install -i tmp logstash-devutils

I am getting below response

ERROR:  Could not find a valid gem 'logstash-core' (= 5.1.2.snapshot1) in any repository
ERROR:  Possible alternatives: logstash-core

PS: I have already installed logstash-core