To obtain a death certificate for someone who passed away 30 years ago in Tamil Nadu, you'll need to check if the death was registered with the local registrar. If it was, apply to the concerned authority (corporation/municipality). If the death wasn't registered or records are unavailable, you may need to consult a local lawyer. Unregistered deaths can be registered via an Executive Magistrate's order with a late fee. You might also need to approach the RDO with evidence or request a 'no entry found' certificate from local authorities to proceed.