Am I wrong or did they used to do a large as well as small and medium? Couldn't find any sign of it on their site if so. Has anyone managed to get a drybag larger than 8 litre to fit comfortably in a medium?

Not sure whats been available, but... 8L is pretty big. Do you really need something so volumous?

maybe not. Current set up is 13l dry bag strapped to the seat and a 20l back pack. The bag strapped to the seat is little unstable and I want to get more kit off my back and on the bike. I've ordered a top tube bag and a tiger so was hoping the 13l would fit in the tiger

I guess it would depend how full it is too. Full to bursting it might struggle.

I believe a large was in development but nothing in production yet.

The issue is when you go over a certain size you start to get a wagging effect when pedalling which is what the smaller Tigers overcome. I use a 8l bag with mine (although its only about 6l full) and I wouldn't want to go any bigger.