The normal method for this insurance is to call an insurance company and ask for excess deposit insurance. This should be your first step. But, it seems very strange to me that you are beligerently asking people on the internet for financial information that you don't appear to need.
1. Understand How a Depositor Bond Works [1]
2. Depositor bonds for FDIC-insured deposit accounts [2]
3. Excess Deposit Guarantee Surety Bond [3]
4. Bond Penalty: Based on Coverage Requested Excess FDIC Limits [4]
5. Hello old friend – The reappearance of excess deposit bonds [5]
In summary, the Depositor Bond provides a third
party guarantee (from the insurance company who
is called the Surety) that deposits will in fact
be returned to the depositor. Depositor bonds
are designed to be “Excess FDIC Insurance
Coverage” and coverage begins at the point where
the $250,000 FDIC insurance obligation ends. [1]
[2] https://www.travelers.com/iw-documents/surety-bond/59375-dep...
[3] https://surety1.com/bond_info/excess-deposit-guarantee-suret...
[4] https://suretyone.com/bank-depository-bond
[5] https://www.cuinsight.com/hello-old-friend-the-reappearance-...
The other links say similar things. This is something banks can buy, to provide extra coverage for their customers.
People here have been arguing that SVB's customers were negligent by not purchasing their own third-party insurance. I think it's reasonable to ask them to support that argument, even if I'm not personally in the market. Supplemental insurance like that still does not appear to be available.