Digital Speedos in the UK had one but no longer list it. But if you ask I am sure thay can help.
Would sit like this 3rd gauge.
I cannot remember if the ECU tracks Oil temp (my guess is yes) - but if so there is always this option. » ScanGauge II others have fitted and used them in the past. Just plug into OBD port.
Maybe one of the Scangauge users can chirp in. But I will look out the ELM and see if Torque sees Oil Temp.
Also I have a VI guage that is for OBD-2 - it powers off even if connected all the time.