It's all I can find in 10W40 synthetic.
If you can grin and bear it, Walmart. Look for 4QT jugs of Shell Rotella T6. Buy an additional quart to make the 5 you'll need, or better yet just buy two 4QT jugs and keep the left over oil for topping up and for the next oil change. They also stock M1 5W-40 (look for "diesel truck" M1 in that viscosity) but it is more expensive and not worth the extra $ over the Shell in my view.Where?