Ping Touratech for the parts. Their metal guards are quick detachable and use the same system.
LINK
They don't list the part numbers, but I suspect you can order them. They typically sell parts for everything. I'd not tell them I wanted replacement parts for my Yamaha headlight guard though, I'd say I wanted them for my Touratech guard and see where that goes. You could probably get a picture from an inmate here if you needed "proof" of you having the product, if not just attaching a pic of the split rubber part to your original request didn't do the job. ("It was on the bike when I bought it used")
The other thought is to contact a Canadian Yamaha dealer, since they were allowed to sell those back in '11 even though the US dealers couldn't because of no DOT approval.