I've been receiving more quotes than in the past containing endorsements excluding coverage for condominium/PUD construction.

Right now you have $1,000 in cash flow that can be used to fund other projects (seed money), pay you in profit to supplement your lifestyle, or fill in any gaps for underperforming properties.  

Quote from @Carl Rowles: When you insure a SFH rental property, do you try to adjust and of the coverage amounts?

It willapply to the other 4 coverages.

How much will the increased cashflow supplement your anticipated SSI?

I do have additional coverage for the sewer since I knew it may have issues before I bought the property. 

There are some that provide coverage but of course the premiums and higher. 

With that in mind, I’m considering purchasing four rental units over the next four years to build a stream of income that could help supplement my retirement by age 68.The challenge I’m facing is that the deals I’ve come across so far don’t make financial sense.

The policy was $2200/year ($1.1M Bldg coverage and $1M Business liability coverage in this apartment LLC) and I haven't had a single claim in my past 5 year history.

You might have other options to explore to drum up liquidity (HELOC, Margin Loan, Policy Loan, etc) that can supplement your HYSA in the DP.