Also try Ebay Australia (not US ebay) with the search filter on the left set to only show items in Australia, and search for "Transformers" in the main Toys listing, or "lot" or "junker" in the Transformers section of Toys.
People who don't know much about Transformers, or don't care, will throw up lots of toys without any specific names or descriptions, so be vague with the search terms.