The Ridgeline has a transmission cooler (all trim levels) from stock. An engine oil cooler would have to be aftermarket.
I've seen people bond aluminum heat-sinks (with fins) to their oil pans, but that might take away ground clearance. You can get them at local speed shops.
Not sure why you feel you need one - there haven't been any (to my knowledge) reports of oil-related failures from Ridgeline owners.
Chip H.