How to find data on Unit Mix of a property not listed for sale

[Chris Scott]

First time poster here. Hi everyone!

I have designed a direct mail campaign to hit 5+ unit owners in a target city near me and I am running into a roadblock. 

I have my farm of addresses and owner information but I have not found any data about the unit mix of properties; specifically the properties that have never been sold on the MLS.

I have used my county assessors website and paid for reports but have yet to get a report that even includes a room count let alone the mix of studios, 1 bd/1bas, 2 bds, etc...

I understand there are other strategies to direct mail (like yellow letters or similar one page letters) but my goal is to hit a specific city, 5 to 40 units and include a market rent analysis of their property in the package i send to owners.

Does anyone know of solid data sites or strategies for obtaining the unit mix of a building?

Thanks BP!

-Chris

I am a licensed RE agent in CA