That injector does not look anything special. I suspect that if you undo the nut, you'll find it is a compression ring holding the injector in place. I've seen many, many injectors - and never have I seen any that look like that.
The best starting point, is to pull the injector, note down the numbers on the injector (on the top yellow housing), and google them for a different (OE) aplication. End of the day - I doubt Magnusson would have had an injector made, they'll have sourced one of a suitable flow rate from an OE motor, and modified the end to suit their needs - ie quick and easy. I suspect the solution they used is not the pinnacle of tech, but a pretty basic (read easy to replicate) approach.
If you can't replace the injector mounting compression ring, you can easilly find superior injector mounting clamps, rather than that nasty looking compression fitting - You'd just need to get it TIG welded in place, but it'll allow you to easilly remove and re-fit the injector in the future.