About a year ago, http://www.sclubricants.com/ carried Delo LE 10W-30 in 3 gallon cases. I can't remember the price. By the time I spoke to the rep, I found Rotella T 10W-30 closer and haven't exhausted my stash. They have 5W-40 syn too, which I've started to see in O'Reillys. Southern Counties even had CI-4 15W-40 in 5 gallon pails (at least back then).
Good luck.
Quite a few good HDEO's are supposedly available in 10w30 but finding them in gallon jugs anywhere is near impossible other than Rotella, and you have to look for the Rotella but at least it's out there.