I don't think NuTone made 40" hoods, there were 30" 36" 42" and 48"
Well, the Frigidaire hoods for 40" Flair ranges were 40" and probably made by NuTone too.
BTW, these can be shipped for a reasonable price. Last year, I bought a 48" NuTone V50 hood on eBay and had it shipped to Vermont and it wasn't that expensive. Of course, If I had paid only $20 for it, it would have cost a few times more than what I paid for it!
Here's what it looked like when it was installed in the previous owner's kitchen. I haven't installed it yet!
Standard hoods don't come 40" wide, as that would not line up with cabinet spacing, which is on 3" increments. The nearest standard kitchen cabinet widths are 39" and 42".