Out of the 20 letters I've sent, I've had 1 guy get back to me and we were in discussions but weren't able to find a price that worked for the both of us.The issue is that I only have a few houses on my mailing list so far (just places I've walked or driven by that caught my attention), and blindly searching every street and address # to see which houses are actually legal multifamily will take forever and doesn't seem efficient.I know the data is publicly available, I just don't know how to aggregate it in a way that would be efficient and useful for blasting out marketing mailers.Are there any websites that can pull massive lists of all multifamily houses in my area?

We saw neighborhoods revitalized when the city allowed for more mixed-use and multifamily projects..

I would consult a lawyer and listen to his advice but where I would try to direct this is the lawyer write letter to HOA that they do not agree with the HOA interpretation that the current CC&R does not allow STRs.  

Ive gotten mixed answers

I've had success with letters, driving for dollars, and off market deals.

In fact, most cities will send a High Usage Warning letter.

Regarding Chicago, the 2024 property tax re-assessment in Cook County should cause some inventory to hit the market, specifically on the mixed-use and multi-family side of things which will be hit especially hard.

I've run into my first issue, in that, the potential tenant has a mixed breed, no surprise there.

I'm looking at a mixed-use property (cafe on bottom floor, 2 apartments above) with an asking price of ~850k. 

You should be asking for any kind of pre-approval letter as well.