http://www.fae.es/en/products/oil-pressure-switch

Try somewhere like this (but closer to home 🙂) ..... they have normally open oil pressure switches in their catalogue .... with a T piece to run the second switch you could put an ignition switched +ve onto one side of the relay coil and use the switched earth of the new oil pressure switch to operate the relay and switch the 'engine running' supply you need.

Bit of a faff but it would solve your problem ... and it's not that easily solved using anything on the normal car loom

K