You could also try a local boat upholstery shop... if you are near the water, Here is Seattle they are everywhere, much cheaper than auto upholstery shops, work with the same materials, and can use your current cover as the template for a new one. Their core business is making custom covers for boats... so in Seattle they have the most talented and experience workforce.
Luis nailed it. But just for ha-has call IM and get a price.
Then get a quote from a couple boat top shops.