I know this doesn't help the OP directly, but in the northeast NAPA carries it.
Well, I had called one NAPA store who told me Northern Tool had it(They Don't), An O'Reily store told me, they had never heard of it.
The NAPA in Colfax, said I don't carry any such thing. But Go see Rick at Bird Haven(about 3 miles out of town). That's kind of a grin, we are experiencing flooding in the area and had to drive 12 miles to get to his place and find roads not flooded.
Rick supplies antique and Classic auto Restorers as well as antiques tractors restorers, from all over the Country. He did not have Por 15, but sells KREEM instead.
He said he knew of at least 200 tanks with it in without a problem. So I bought a quart and will give it a go.