A non-academic group to which I belong holds military history conferences a few times a year. We've discussed seeking presentations from graduate students, but we're unsure of the process. So, I have a few questions that might be answerable here.
Where would one publish a "call for papers" on specific areas of military history? (Our conferences are on Operation Dragoon and the Battle of the Colmar Pocket in WWII.)
What would be expected to be provided for presenters who are accepted? We're a non-profit, funded only by fees for the conferences, so have never budgeted for honorariums, lodging for speakers or their expenses. Would that be so uncouth as to inhibit anyone from responding?
Would sample presentation videos be excessive? We've had some presenters in the past whose style has been so dry and non-interactive that the audience became disengaged. So, before we would accept a speaker, we'd want to see video or a live presentation to ensure that they will meet our needs. Is this excessive?
How long a presentation would be acceptable from the speaker's perspective? I expect we'd be interested in presentations of 15-20 minutes, as the topic would be rather specific (such as a presentation on the actions of a single military unit rather than on the campaign in general).
Basically, I want to know if our expectations don't meet academic expectations, so we can decide whether to modify our expectations or decide not to issue a call for papers.
A couple additions to Ben Norris's answer:
Understand that, unfortunately, lots of people will regard your invitation as spam and ignore it. You can't help this, try not to worry about this too much.
If you can't fund the speakers' travel, say so. In my field, it is customary to pay the travel expenses of invited speakers, but if you can't then it is fine to simply say "Unfortunately, we will not be able to provide funding for your travel expenses" in your message.