You probably can't find it.
Pennz Longlife is diesel engine lube, and diesel 10W-30 is generally only for very cold weather use. If you vacation in North Dakota or Minnesota, look there. You might find cases of gallons; more likely drums.
Good luck finding any 10w-30 heavy duty oil. I live in michigan (detroit area) and could not find any. 15w-40, 5w-40 and sae 30 are the only things I could find. I'am sure it is out there, but I can not find it.