I have not seen an expanded capacity tank for the newer bikes.
With the newer EFI bikes, the fuel pump and such are located inside the tank which is a single tank rather than a pair. I would think an expanded tank would be a much bigger engineering issue than before.
You can add an auxilary tank. Like these guys:
Tour Tank Auxiliary Fuel Tanks for Motorcycles
Those are set up to pop on and off to be used only when you want the added capacity. Or, you can just buy a couple of 1-gallon cans and keep them with you. There are cans out there designed to fit in a saddle bag.
If you are set on a bigger main tank. You might be able to find a used stock tank somewhere and work with a custom shop to cut and expand it. Since it is going to be cut up anyway, you might be able to get a cheap one that has the paint beat up or a ding here or there.
By the time you get it fabricated and painted, it won't be cheap, but you'll have what you want.