there are none
In the case of the Tyrannofex and Tervigon, most people start off with your base Carnifex, and mold Greenstuff on it until you get a decent conversion.
Its fairly simple for the two aformentioned models, for a Tervigon you simply need to mold an "eggsac" or a "birthing pouch" on the underside of its lower abdomen, and for the Tyranno, just stick a really big gun on top of its carapace and you are good to go.
For more specific ideas (and a few tutorials) i would check:
http://www.dakkadakka.com/dakkaforum/forums/show/8.page
http://www.dakkadakka.com/dakkaforum/forums/show/56.page
http://www.dakkadakka.com/dakkaforum/forums/show/68.page
if you decide on not going a conversion, using just the bits that come with most monsterous creatures you could do some light modifications to the Standard Carnifex and ask your opponents to allow you to use them as 'count as'