Not knowingly, I guess. A chow chow/rough collie isn’t a breed, so I cannot say whether I’ve encountered one or not. It doesn’t appear to be a ~designer breed~ either, so your best place to get on is an animal shelter!
This may be a weird question but have you ever seen or heard of a Chow Chow x Rough Collie dog? All I could find with Google were Chow Chow x Border Collie.