The answer is relitively simple. IF your group - Galactic Knights, 501st, Mercs or however is trooping an event then have your command staff check with the organisers beforehand to ensure that you are exempt for the rule that applies to the general public.
I don't know how it works for other countries, but here we "work" the event - so we don't pay to get in and we aren't subject to any prop weapons restrictions. Perhaps that's the way to go.
IF the event organisers turned around and said to us "actually, you can't carry those weapons" we'd not attend. IF we had arrived and they then said that then we'd leave.
Whilst it sucks that they are doing this to all costumers - it should be possible for those in various groups to get around these kind of rules.
