If you're looking for Ruby folks, go where they go - local meetups. Second would be online but you will need to mine Stackoverflow, Github and similar sites and realize that they get approached regularly so start engaging early (at least 3 months before projected start date.)

Yes, local meetups seem to be key here in Toronto as well. Groups like Ruby Pub Night are the best source for local Rails developers.

After that, certainly there are lots of online options, particularly if you're looking for remote work, but few of those are very specific to Ruby.

DevTeam. Space is a great choice if you want to hire a Ruby on Rails developer.
You can read more here: https://joshfechter.com/hire-ruby-on-rails-developer/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath