Are there any buses from Pattaya to Khon Kean that do not go via Bangkok

Yes!

Buscompany 437, at least 4 buses a day

Chan Tour, same

Nakhonchai Air had some buses, if they still do?

Maybe Esan tour still does the same.

Yes!

Buscompany 437, at least 4 buses a day

Chan Tour, same

Nakhonchai Air had some buses, if they still do?

Maybe Esan tour still does the same.

Yes, Nakhon Chai Air has several buses a day. They are on 3rd road, about 100M north of Central Pattaya Road. But! Relatives do this route fairly often. It does a LOT of local stops. If you want faster service, go to Bangkok and change there. That's what my wife does. But her mother does use Nakhon Chai Air as she doesn't want to change. Up to you!