I don’t think David Manners, et al have modern replacements for the dampers.
There are normally a few on eBay – there are couple on there now.
As you likely know, the damper is basically two steel discs bonded together by rubber & was manufactured by the Dunlop ‘Metallastic’ division. I’ve read of dampers where the bond failed & the outer disc came loose. It’s never happened to me, thankfully. Unless exposed to extreme circumstances, degradation of the rubber is likely to be limited to a few mm from the surface. There’s a lot more bond area below this layer that ought to be fine & give years of life. Worth inspecting a secondhand damper carefully though, to try and spot any obvious weakness; maybe by using a flat screwdriver to stress the bond slightly to check it’s still sound all around the circumference.
Having a damper will also give you the official timing mark, of course 🙂
Good luck
