And more ideas are welcome by anyone .... Let's make a really good topic which can ease of searching and sortlisting efforts of recruiters of the community.
Sending them personal messages may be a great idea, but we have a forum rule about message spam that can lead to a temporary ban, so my advice is to drop a meaningful comment on the service provider that you want to invite to this discussion, and ask after your meaningful post if they are interested to include their service to your topic, and if they are interested they will respond and that's the time to send them a personal invitation.