You don't need a "casting" to hold a scrollsaw blade. It's hard to tell the demensions of this blade holder, but I have made some for my saws. Just take a 1/2" square x maybe 5/8" long piece of steel (available at the hardware store) ,drill and tap a hole in the bottom for your stud. drill and tap another hole ( for the one your set screws go into ) , then drill a small hole (maybe 1/8" ) in the top for your blade to go into. This hole should be about 1/2" deep or so. Screw one set screw into each side up to the blade hole ( use a little locktite on one hole) , insert blade into 1/8" hole and continue to screw each set screw from both sides until blade is centered in hole. You can even grind the end of the set screws flat before inserting to rest flat against blade.
Taps are cheap, and you can use a wrench as a tap handle if you don't have one. Use cutting oil while tapping, and tap a turn and back it off and go again .
later Daniel