Once again, a typical case of crap ESA and its effect on chain and dynamo sprocket failure. So my advice, weld up the crap ESA or get a belt drive - which got no ESA at all. Or else, as long as the Spares Co is ignorant for redesigning the non-working ESA for a real thing you could do a cush drive for the dynamo sprocket. Speaking about cush drive, you don´t need any in an all chain drive on a motorbike. What exactly do you want to protect with this ?? Chains are nowhere hard in action so not much reason for having them. In a Vincent the gearbox teeth are extremely solid and I have never seen proof of worn teeth in there. BMW or Guzzi got no chains anywhere so all gears which may be harsh from wheel loads or from crankshaft "shocks" . But still no cush drives on these, just effective ESA in gearbox input shafts - well, not so much on some Guzzis, similar to the Vincent design.
Anyway, the wrecked middle row of chain rollers is not due to "high" loads from the dynamo - just 1/4 hp max, but from the mass of the rotor/armature, loading the rollers from shocks entered into the triplex chain by the ESA bashing onto its stops each time you open or close the throttle.
What you could do for alternative to unavailable effective ESA, do a cush drive for the dynamo sprocket. I did an exercise on a "limited slip" sprocket hub for the brushless alternator, just for the fun of it. Would not actually need one as I did my own ESA in BMW style. But maybe the wave washer loaded friction drive in the sprocket hub could lead to ideas for your mod. Another design could include some fat o-rings in holes in the sprocket for damping peak loads from the rough operating conditions in the triplex chain.
So when taking care of the dynamo drive there should be no more troubles like seen here and split rollers are quite acceptable basically as the outer rollers are fine with all power from the crank. Quality chains in high tensile steel - who would produce anything low strength for trade use ? I would not think you could keep costs much lower by having "cheap" steel types for substandard chains ?
Vic
mass of rotors comparison, small diameters are brushless motors, one Miller armature, one 3ph alterator BMW:
"limited slip" cush drive with phenolic paper friction material plus wave washers:
BMW style ESA :
some shaft drive Jap ESA - they copied my BMW inspired three lobe mod !!