BMW use electric water pumps on their 35i engines.

I am looking at using one possibly in conjunction with the mechanical pump.

All the usual suspects though do not flow enough at a decent head. For instance you show a Davies Craig 1bar and it doesn't flow anything.

The BMW pump is a Pierburg cwa 400 and needs a CAN controller otherwise it runs at 95% permanently. It needs 30amps to run! The controller you can use is here