None look familiar, but I only used it once so my memory of it is limited.
isthereanydeal looks a mess after searching for Sins of a Solar Empire: Rebellion, Stellar Phenomena.
Two separate entries covering only three suppliers. Doesn't mention GMG in there, who have the DLC, and doesn't include GameStop (Impulse) as a supplier in any searches - they don't have the DLC for this specific search.