switch625,
Alas, the Surefire Responder is arguably the penultimate in shotgun weaponlights. Merely clamping a Surefire or other light to your longarm will not give you a combat-reliable light as the Responder, as that unit incorporates three shock-proofing features that are not found in typical non-weaponlights:
1. Shock proof bezel -- cushions lamp from slamming into the lens assembly;
2. Machined "shoulder" in light body -- prevents batteries from slamming into the lamp assembly;
3. Buffered multi-cell batteries -- prevents battery cells from slamming into each other.
Lose any one of the three and you could end up with a dead light due to weapon recoil. Weapon recoil might not be so bad with a 5.56 NATO gun but we're talking 12 bore whomp here. Recoil proofing a weaponlight to be used on a shotgun is all that more important.
However ....
If Mark Penman's website was still up, you could refer to his article on his own improvised Surefire mount which I believe he made for his Beretta 1201FP. Mark took his own life recently so I expect his website is no more. Anyway, he used a hose clamp and various Surefire parts to create a makeshift but serviceable weaponlight, at a much reduced cost over the pricey Responder.
You may be able to do the same -- IIRC he took a Surefire 3P, replaced the bezel with the Surefire shock-resistant bezel and somehow hose-clamped the light to the fore-end. This solves all but one of the recoil problems noted above -- the sole problem remaining is that the 3P's light body does not incorporate the machined shoulder to prevent the battery from crunching the lamp assembly during recoil.
Justin