You can filter the list by pals that drop that oil and then you can click on them to see where they spawn. Relaxaurus are numerous and drop it, but they also hit hard in the wild
I remember when my base got raided by Relaxauruses, I got one-shotted three times and my house was set on fire, had to relocate it to the second base. Thanks for the resource!
You can get it from the rock whale things. I think they were called damuds?
You can look at the paladex and see what drops what (if you've caught one at least). The thing that needs the oil isn't learned until level 24 anyway. I'm at the same point of progression.
I've gotten some from those cotton candy pals, killing the giant green mammoth, really the pals you release from the cage just drop whatever they drop on death just like catching any pal, so if you find them in the wild they should also drop it.