Yes. I am near OK City.
I am looking for such a yard myself. As you probably know, about 5 or 6 years ago the local EPA office went around to the salvage yards with a list of regulations they intended to begin enforcing. A lot of the smaller yards that dealt with older cars and trucks just folded and closed rather than go broke trying to comply. Another unintended result of high-minded legislation. By trying to clean up the environment, the EPA has radically reduced the number of operating salvage yards. That means fewer recycled parts and a net increase in pollution as new parts (or even whole new cars) must be manufactured to make up the difference. Sad.
Pull-A-Part in OKC had a 520 a couple of weeks ago, but it was pretty well picked over when I saw it. I did get a couple of headlamp rings off it before they crushed it. They keep the older cars in the far northwest corner of the lot.
There are usually a couple of 720 pickups in the "Import" section in the Northeast section of the yard.
I have yet to see a 620 or a 521.
Man, if there is nothing in the Chickasha area, I'm not sure we'll find anything in this area.