I have 2 fuel bags of 8 litres each. I've used them in Australia and Africa.
with special lids, they cost something silly like £30 each. they're not really any better than jerries, but it might be an option for under the seat or in a tank bag or rucsac if you're terminally insane.
as for bigger tanks ... I've never heard of one for your bike. you'd best get a damaged secondhand one and have that modified - cut the top off, weld in a band and weld the top back on, but make sure you consider reaching over the top and the cut outs for the handlebars.
frankly, I'd go for the fuel bags as they fold away to nothing when empty. and they're dead tough - we played football with one half full and left it in the sun for ages to test it.