Is it possible to get oxytocin from a natural source?

No. Oxytocin is produced in the pituitary gland. Recovering hormones from humans (or animals) is associated w/ many risks. So there is no good reason to attempt to extract from living or dead persons/animals. To my knowledge, this is not being done anywhere. Oxytocin is a relatively easy protein made in the lab w/ the identical Amino Acid sequence found naturally in human beings -& it works perfectly.