This one has a built-in seat bore as part of the casting with a viton seat insert and a retaining spring clip that snaps into a groove above the seat. I wish it had a removable seat like so many carbs have. I'll try to find another if I can't fix this one.
If you can't repair yours, you could basically buy any Walbro LMB new or used carburetor and use the body with your other parts. Walbro made literally millions of carbs in so many configurations that you shouldn't have too much problems finding something that would work.
And if worst comes to worst, you could buy a new needle and set configuration for a more modern design and drill yours out carefully and insert the entire setup in yours. It really isn't that difficult.
One other things you can try, take some fine valve grinding compound and a few cotton swabs and rotate them around to polish the seat area. I've actually done that on one carb and work very well. I used a Dremel tool and cut the cotton swabs in half and used polishing compounds to clean and redress the seat. It came out like a mirror and no leaks either. Just an idea.
