For someone wanting to carry a sidearm or a full-size rifle, I would recommend a Rubber Band Gun. I've been using a rubber band gun as my sidearm for my LAPD uniform/costume for the last four years, and I'll be using it again for my NYPD uniform/costume this year. Not only does it give you something to rest your hand/arm on when you're doing nothing more than having a wobbly-pop or two, but you have an elastic projectile if you decide someone needs being pelted with bits of rubber.
As a disclaimer/recommendation though, I highly suggest leaving the rubber band gun in a natural wood colour versus black. If you opt for black, someone may think that it is real and things would go bad very quickly.
Speaking of which, I'll post pics as soon as we get them done.
South Manitoba Rifles
Non Sibi Sed Omnibus
Age Verifier - Manitoba
WE C7A1 x2 - WE M14 DMR - WE L85A2
CA C8 - CA SLR105 - TM FAMAS
WE Browning Hi-Power - Tanaka Browning Hi-Power
WE M1911 - KWA SIG Sauer P226 - KSC SIG Sauer P229