Dave makes them, not sure if he has any allready made. The one I made uses a Dog Guard available from Halfords and takes about 1 hour to make / put on the car but isn't designed to withsand any impact, just gets you through the SVA.
If you want to make one you need the aformentioned Dog Guard (this is actualy sold as an extension to their dog guard costas around £20) you then need two lenghts of tube about 30 cm long and 15mm diamiter, then you need to weld a flat metal strip the the end of the tube about 2 cm wide and 7 cm long (this is to fasten one end of the tube to the bulkhead you will need to drill a couple of holes and use some 6M bolts, look in B&Q they sell some metal braces that are powder coated. You could even get away without needing to weld by using some chemical metal as the weekest part in a crash is the aluminium.... The other end of the tube needs to be welded / stuck with Chemical Metal to the dog guard. Finaly cap off the holes in teh dog guard with some nut covers,
I also drilled and rivited the guard to the size i needed