I'm not aware of any CS pets referred to or based on mythological Rocs, if thats what you mean. The closest thing I can think of right now are the griffin western dragons from 2019, there were originally PPS ones and a few grown versions released over christmas;
archive/2019/Fae%20Mischief/Western%20Dragonarchive/2019/Christmas/Western%20DragonThere might be others I'm not remembering right now, but since Roc usually (from what I know) have natural bird patterns the main difference with them will be size, and since lineart size itself doesn't usually get modified, those are probably the closest in terms of 'giant bird'. There are various bird edits of other linearts, western dragon is just one of the largest. If these aren't what you are looking for and you are thinking of a specific design, it might help to describe it, especially if you remember what lineart was used, that will narrow it down a lot.