To be fair, many English speakers are not familiar with the word "dowser" A couple years ago I had a similar issue trying to find what I had always referred to as 'stage brakes'.
That was just what they referred to them in shop I first used them in and that's the name that stuck with me. The funny part is, the local hardware store kept them in stock since we bought so many of them and had them on the shelves as "Stage Brakes".
I'll vouch for the #1 google result, the City Theatricalunit. We have 2 in different spaces, and they both work great. My only nitpick is that we have nothing else that needs powered DMX in the booth, so it ends up eating a whole universe.
Stage brakes are what I'v always called over center levelers. Used them for orchestra shell towers - one each corner and they lift it up and can be preset to level it even if the floor is not. Over center clamps is a good google term.
Back to the original question, you might want to check out Engineering Solutions Inc at: Engineering Solutions Inc They make a bunch of different products including dowsers.