HI. A while back I have used an RIA for oxytocin. I think it was GE healthcare but used to be ICN Biomedical. For AVP you might try Cayman. Also, another favorite kit company of mine is Arbor Assays out of Michigan. I like their kits and tech line.
It was a long time ago, I do not recall. It may have been both but at least plasma. Please check out the online protocols for these assays. They will list the viable sample types.