Have you gone to a plumbing supply store and shown them a photo?

Franke still makes a sink that shape in stainless, single bowl.

You don't have to find a sink that is the same exact shape - it just has to be larger than the current cut out.

@Joseph Corlett, LLC - is an expert in this area. He has posted MANY sink replacements/updates that he's completed. The new sink always makes the kitchen look updated. He doesn't remove the countertop - but is still able to reshape the opening. Maybe he will see this and be able to provide some guidance.

"Franke still makes a sink that shape in stainless, single bowl."

I can't imagine Franke making any version of an American Standard sink.

HU:

Here is a Kohler 3821 undermounted into your cutout. It's a half day job for someone with experience.

Here is the same sink with the cutout changed to fit perfectly. That's an all-day job, plumbing included.

Your sink and cutout are obsolete and discontinued; searching for an exact replacement is a fool's errand.

What state are you in please?