This has been on one of my project list, but for round carrier aftermarkets swing arms, OEM you can just run a skid plate, Ill give them a call this week.

mitch you putting your hand in the cookie jar again.

John, more curious to see if they can be made for a round carrier, also if they would make a Bling Star type Sprocket Guard.
http://www.motosport.com/atv/BLINGSTAR-DUAL-SPROCKET-GUARDS

I'm sure there are enough of us to justify getting a small batch made up?

Possibly both, depends on price.

A valid point, but how many rotors and sprockets do you know of that have been balanced?
I doubt the inertial moment of a guard that diameter and weight would create any perceived vibration issues....much less at the speeds a dune/trail bike normally sees.

A skid plate is simpler in construction and does the same basic thing (perhaps a bit heavier?) except for a loss in ground clearance and preventing chain derailment like a sprocket guard can.

Now, for the sprocket guard, instead of having it rotate with the sprocket, why not a similar approach as the rotor guard?
If you had it extend over the sprocket covering the chain, from the point at which the chain meshes with the sprocket to the point it departs, then you'd have what amounts to a case saver for your sprocket.
The chain wouldn't have a chance to derail, the sprocket/chain would be protected, and no additional rotational mass or the unlikely vibration issue.
Have to admit, the blingstar sprocket guard looks pretty sweet, but it looks heavy as ****.
Maybe some cutouts or lightening holes would be a good idea.

I run similar setups on a Apex mini Quad with a CR85 engine. Shark fin for the brake Rotor. and a one sided Sprocket guard. I would run a single sided sprocket guard and DB chain guide, just like on the apex. I do not like the dual guard on the sprocket Ive seen a lot of broken cases from chains jumping onto the inner ones also mud builds up in them when there dual sided.
As far as weight being an issue, are you Drag racing all day or riding, this apex races through the woods and water for a hour at shot and you cant feel a difference.