I bought the solid stainless steel mirror arms at a local aftermarket parts house in Wichita, Ks. called " Truck Stuff". Catchy name huh, LOL. The parts themselves came from:
Delbar Products, Inc.
Perkasie, Pa. zip 18944
Part # 620C-11 Price was $18.00 ea. plus tax.
That was several years ago, inflation most likely has them over $20 now, not sure. May be able to find them doing a Google search or check with your local parts house to see if they can order them. Highly recommend them over the rusty/crusty originals I had to start with. Hope that helps.