In regards to getting a new lens it doesn't even have an individual part number as you said so yea the only thing i can think of is getting lucky and finding someone who is either making a track bike out of the R3 and no longer requires the stock headlight unit and is nice enough to give you that specific part or finding someone with a wrecked bike and hoping for the same thing.
Apart from that if you post a picture with the extent of the damage it could help generate ideas