Do you see the horizontal posts with the notches sticking out? Well, on the back of the two TVs there's an adapter plate that mates up to those perfectly.
So, either the previous house owners are a bit dim and just unhooked the TVs, or they were stolen before the house was sold. The lack of any obvious damage suggests to me that the TVs have still got the plates on the back.
If the owners left a mail-forwarding address then get in contact and see about getting the plates back. The brackets are part of the fixtures and fittings, so by rights you paid for them as part of the house deal. Also the plates are useless on their own as are the wall cantilevers. So they might as well return them because they're no damned use to either party as it stands.
Before you ask about spares... No. Don't waste your time. Stuff like this is mass produced in China. They don't give a stuff about supplying spares. It's a volume business based on whole product sales only. That's why cantilever brackets sell from £40 on Ebay and not £140