Angola canvas has a pattern for the C-Dory 22. They are easy to work with for changes/mods to their standard pattern. Don't know about the 23, but it might be the same pattern.
The cover for may 22 was about $1100 including a couple of custom mods and a sending it back to get another custom mod done.
FWIW, tell them to extend the skirt of the cover about 28 inches or so (depends on your trailer). Have the cover extend all the way to the trailer fenders, not just to the rub strip per the Angola pattern. It's not that expensive to get it extended. But you'll save on shipping if you have it done from the get go vs. having it reworked.