Hey Impossible Tom -
We reached out to Classic Accessories 2x via phone / VM and 2x via their Contact Us page regarding custom covers a couple of years ago, but we never got a reply 
After thinking about it for sometime, I think the word I used that scared them off was “custom” as there is A LOT of work that is required to make a custom cover (CAD, patterns, cutting / sewing, etc…) When it’s all said and done, a custom cover could easily run you $800 - $1500. And in that amount of time they spent on the custom cover project, they could have used those resources for larger income projects. It’s understandable…
Either way - we can’t have a standard “One Size” cover for our pizza ovens for one reason… No two ovens are identical (unlike mass produced pizza ovens). So a cover that fits Oven A, wouldn’t fit Ovens B - Z.
On the flipside, let me share with you a FANTASTIC Organic Masonry Sealer that repels water from penetrating your pizza oven.
https://store.brickwoodovens.com/eco-advance-organic-masonry-sealer/