Hi Racer490:
I think the GMC C-15 and Chevy C-10 lower control arms are the same. I am surprised that in my collection of paper catalogs that only one catalog lists the lower C-10 control arms.
Other alternatives are get one from a salvage yard or to find the OEM part number and see if there is an NOS available. You could google the OEM part number. You should be able to find the part number on an on-line GM parts catalog or there may be one on the tech section of this website. One of my sources for NOS is Phillips Muscle Car Parts...they are on the web.
Good Luck,
Henry