I haven’t seen a replacement for the upper perch. If you can get a nut on the shock bolt then it is probably OK. If you really want to fix it I am getting ready to scrap a tub that is rotted out, but the front clip is good. If you want the upper spring perch let me know. You could cut / grind out the one on your car, replace the threaded back up plate or weld in a new nut on the existing plate (may make more sense to maintain the front end geometry), and weld in a replacement perch. It really depends on how far you want to go and whether or not you want to go through the aggravation of getting to the nut the next time the shock needs to be removed for service. I’d say run it as is.
Chris