I would suggest choosing a date and posting that. Once you are ser up to have the training, just send everyone invites and inform them of what you are doing. Many will probably stay and participate. It is quite possible that many didn't see this post but would like to participate.
What maps are you planning to cover. If the call outs are available, I'd suggest doing the newest map pack. The original maps have been done at least twice.
I actually posted twice in New recruits and Combat Training I was planning on all maps up to the newest untill those become available as we have quit a few new members I did a 1on1 with General PO and he stated he didnt know what we meant when a call out such as A-DOM B-DOM C-DOM was called I will work on a idea to attempt to get more of an interest