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.
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.