Jacek,
I bought the Tie rod ends for my C8 from Jim Carter (OldChevytrucks). Just like you I wasn't having much luck searching for a replacement using the part number. In the end I just asked for the diameters of the treads and the TPI and found a match. I bought ME348L and ME348R; suitable for the C8, but I think those for a C15 are heavier.
Edit: maybe ME537R and ME537L would work for the C15?
http://www.oldchevytrucks.com/cart/i...es=tie rod end
regards,
Alex