Well, I don't think they're gonna sell to well over here on the sunny side of the pond.
Firstly, we want sawhorse brackets that fit 2x4s (pronounced two-byes in Murican), which measure 1 1/2" x 3 1/2", of course.
Also, with your design, weight on the top of the horse will stress the welds. The brackets we have available here at every hardware store are designed so weight on the top of the horse pinches the bracket tighter on the 2x4 spine of the horse.
In addition, we also have nifty folding metal and flat folding plastic horses.
Best I've seen on a job though, a fella made a horse/stool/toolbox combination that seemed pretty darned handy. Seems to me, a fella walks onto a jobsite with a box like that, and he looks like he knows what the possum fur he's doing; other hand, you walk in and start ripping two bys in half to put together some kind of wobley English sawhorse, well, be good for a laugh any way, ennit?
-- Timothy Juvenal