What should I do if my landlord won't provide their ID for my retirement visa extension in Thailand?

Basedon my experiences(The landlord is Thai in my case)

For Non-O retirement visa, we usually submit a copy of the landloard's copy of TH ID card& House registration(House master page)

The usual immigration mess again. Happened to me once, too. They asked for landlord ID when extending my stay. Funny - if not to say stupid, cause I presented them with a fresh TM.30 which the very landlord had to do for me the day before (using his ID). It is absolutely impractical to ask someone for another ones ID - as people are understandably hesitant to pass those around to strangers. Why would they have TM30 as proof of address and landlords identity only to then ask the extending applicant again. Another case of someone at immigration not getting their own work.

All your landlord needs to do is photo copy or take photo of his ID and email / line to you

Which Immigration office asked you to provide this?

I think what is required is a TM30. If you have a lease you should be able to self register.

If you have a legal rental lease you already have it. It's required on a Thai lease/rental agreement (a copy of their I.D. or passport)