SSW..
If you are referring to Grade #3 that were sold by the Tannery Shop, then they are the only one who sold them AFAIK. They typically had deformations, large bubbles and airpockets from casting and were sold cheap. Typically they would get a batch of castings and would sort them according to quality from Grade 1 to 3. The Grade #1 were the ones they sold for $75 or so, with Grade #2 and #3 being cheaper, but requiring more work to complete to overcome the defects.
They weren't something that was always in stock, but availability depended on the quality of the latest casting run. Since William is currently deployed and NOC is selling the lowers in his absence, you'd have to contact NOC to see if they are grading and selling the lowers in the same manner that William was.