We got a large sheet of it from a Chandler but the colour was wrong. However that doesn't matter on our "Lil Dink".
The colours changed fairly recently. So that could be why the one you want is expensive or hard to find.
The amount of hypolon and glue we use on it is truly amazing LOL. It's 10 years old and has nearly circumnavigated! It started in Perth, Western Australia, headed west, ended up in the Caribbean where we bought it. Now its back in Australia and headed on its second lap. Same Mercury 3.3 hp too! Of course I have to repatch another hole in it. We have given up on the floor - its a foot bath
These are great suggestions. I work for DuPont and even was in the Hypalon business many years ago. Just as important as the fabric is making sure that you use the right adhesive. I see that the vendor Ziggy mentioned also offers this.
They sell it by the foot off a 58" wide roll at the Island Water World chandlery on St. Lucia. It's about $50 a running foot at that width. I know that you're not interested in going to St. Lucia to buy Hypalon, but I thought you'd be interested in the comparison with what you've found.