Clifford E. and Lora V. Hoag are in the 1938 Spokane City Directory as living at W 608 Augusta av. If they owned that property, a Spokane County Title Company might be able to find when the property passed from the ownership of Lora Hoag, perhaps leading you to a probate file number. Title Companies these days often, I believe, have direct computer access to county land records. They may do such a search without charge.