We had a very similar dog - border collie /Australian cattle dog mix that we had to put down last year at age 14. Best dog we ever had. Incredibly smart and I don’t think as hyper as a pure BC. Our’s looked similar to yours but darker brown. His litter mates were black and white with one other brown and white.
After reading your description and my own experience I’m convinced this is a superior breed. Perhaps someone would be willing to breed them on purpose?
Hope you have some luck finding another one.
Then you understand, warm, intelligent, loving and always helps you park the car. Aussie trait: circles and leads instead of pushing from behind.