They are not uncommon, but less popular as they are more expensive to make
as each hull has to be fabricated. With a GRP hull once you have built the mould you can more or less bang em out at will, granted that the laminator has to have skill to do a good job but it's a much quicker process.
Ocean Dynamics are probably this counties most known Ali rib manufacturers fantastic boats that they are and there is somebody on Hayling Island making them. They might be called Pepe Boatyard
I also believe that a Canadian company called Carswell industries make them but their delivery time is unbelievably long.