Hi SFS - directions for the Chok Chai land office :-
Travelling from CC towards Korat, go straight on at the traffic lights (where you would turn left for the Zoo and the Korat Resort) and go on for a few km (up the incline) and you will find it on the right in the next few km - the building is about 40 metres wide and 2 storeys, an obvious Govt. office so you can't miss it. Do the U and there you are.
Coming from Korat, Dan Kwian, on your left, I'd guess it's about 2 km past the 4 metre high 'big jugs' at the roadside marking the easternmost exit from Dan Kwian - you can't miss it really on your left.
The land office was moved there about 5 years ago.
I'm fairly sure that's it but I left the area years ago. Good luck
