Most companies that do home AND auto will offer it. The trick (not really a trick) is that the umbrella can ONLY be added after you maximize coverage on home and auto.

Check the bogleheads forum for discussions on insurance.

Chubb - you need to go through a broker and I should note i also have homeowners insurance that has some liability coverage which I suspect also influences the umbrella rate - just find a broker that sells Chubb/aig/natgen/travelers that cater to high net worth individuals (you don’t need to be one! I had a renters insurance policy from Chubb right out of college) But those policies tend to be more customizable - and my experience is that they’re more inclined to pay claims