I have been told by a visa agent that you need a Thai work permit to obtain a Myanmar business visa from the Bangkok consulate. Can someone please confirm this?

Incorrect.

You need appropriate letters and company registration copies for the Myanmar Company (or relevant Myanmar Government Ministry) to facilitate a Myanmar Business Visa.

The form (for applying for the business visa at the embassy in Bangkok) is available here: Myanmar Business Visa downloadable form

There are other threads which detail the required paperwork, please have a look through - however the main thing for you is a Thai Work Permit is NOT a requirement for a Myanmar Business Visa

SVB

Thank you!