Webley Flare and Riot gun for sale on Gunbroker, and only 10 hours to go, and looks to be sold.  Built on a Webley Mk. IV chassis, it also includes a shoulder stock, which in itself is pretty desirable.  It's not going cheap, but should be reasonable.  Downsides: Federal Labs nickel plated everything.  The hammers been cut (I hate it when they ruin a perfectly good Webley hammer, do they think they grow on trees?)  Upsides:  Did I mention a shoulder stock?  Also has a pretty intricate gas round with folding fins. It'll sell today...

Update: This gun sold for $575.00

Webley Riot Gun