LMC does sell them as do a few other resto companies but the offshore replacements dont fit right according to user elcampo in this thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=528294
I found them on rockauto for you, you have to search for "control arm shaft kit" and you have to buy exactly that the whole shaft kit which is a little spendy but worth it for quality suspension parts. FYI I searched for a 1970 C20 350cid. I bought these for mine but Im dont recall if the C10 uses the same or different PN.