http://www.mrmodellbau.com/_shop/product_info.php?info=p619_SU-122i-Russian-Assault-Howitzer-on-Stug-III-Ausf-C.html
About the SU-76(i) I would like to make one but scratch seems the way to go, none of the many conversions on the market looks quite right...
Cheers,
Christophe