Asking for my Husband, Best Place to buy "special" parts for '88 Suburban tailgate?

[OverRunWithSons]

The ONLY place we can seem to find these parts is LMC Truck magazine and this stuff seems to cost an arm & a leg! We are tired of the window falling thru sideways. Looking for "Window sash" and the side "glass channels". Is this the only place known to man to buy these parts? He tried making the sash himself out of stainless, it works fine going up, but not for getting the window down. He is beyond disgusted & I guess the junk yard won't sell parts like this. Got to buy the whole tailgate. Help!