Chris,
I'd try Porsche repair shops… then Porsche body shops...
In my experience sometimes these are good options when the new and used parts places can't help…
Another alternative is (haven forbid) using later (more easily obtainable) oil lines…
From the time 911's started using external oil coolers all the way to 1974 they put something different or changed locations of something almost every year…Cooler types, thermostat location, and how the lines run to each…
I think, like so many others things, they were sneaking up on the different problems: location for convince and heat... and finally got it right in 74' for the G series cars. Part of the proof is they didn't change them again until, man I don't even know, I think all the way through 89'.
The later oil lines have the thermostat just behind the rear torsion bar tube, still accessible but well away from the engine compartment and exhaust.
My car did not come with a cooler …
My solution was/is NOT concourse correct but it gave me the most efficient answer at the time…and guess what? … it's still there!
About 14 years ago I had the good fortune of having someone (Tony Gerase of TLG - Macro's dad) find and install a 72' small radiator type oil cooler (I felt more efficient then the trombone) along with late 74' type lines on my 73'S … no muss, no fuss… and the rest is history...
Just another way to solve the problem...
Good luck,
And Cheers