How do I find all places that SET a property?

You can use Resharper.

Alternately, set the setter to private (Or comment out the setter completely) and recompile. You will get errors where you're trying to set the property.

For what it's worth, this will be natively possible with VS2019.

Specifically the 'Find All References' window has a new 'Kind' column which can be filtered for 'Write' references:

The specific Github PR that added this feature is scheduled to be included in Visual Studio 2019 Preview 2 (16.0.P2) https://github.com/dotnet/roslyn/issues/22545

The full release of VS2019 is roadmapped for Q1 of 2019.