Our company is moving offices but we cannot find anything in the Thai rental agreement that says anything about termination on the part of the occupier?

Its too late if its not already in your current agreement.

Have a look at this one, its in thai and english and has a tenant leaves clause.

 

https://slice-of-thai.com/rental/rental_contract.pdf

 

I wrote the lease for my tenancy with my landlord myself, when we needed something to satisfy Immigration. It's worked well for both of us over the last 6-7 years.

Real estate agents might have a standard template. As far as a government-specified one, possibly not.