I came across a sfh with mother in law suite.

Start on Instagram, tik tok, Facebook.

Problem is that your only remedy here is likely a suit for specific performance (costly and probably not likely to succeed) unless the contract contained a liquidated damages provision. 

I have a SFH, zoned SFH, that has an in-law suite that shares a wall with the main house but has no other access.

I think heloc is better suited for short term investments like a flip.

This is going to depend on the goals you're trying to reach (i.e. it may not be as financially lucrative to fix and flip in CA, even if you're in CA)- so if not in your location, where suits you best (most of the time it comes down to who you have to work with in other areas or purchase price point mixed with ARV)4.

They were a SFH with an in-law suite and the numbers didn’t look good for a long term rental.

Also, if you shop for new insurances definitely go to a broker instead of an agent so your broker can give you multiple different quotes and even get you customized insurance that will suit you best!

They'll also know of loan products that may suit your needs.

And file suit as the timeline permits.