If you can't find one, you can make it out of
aluminium. Aluminium is not hard to work with. If you take your time, you can cut it with a sabre saw or a band saw and a small hand grinder. WEAR EYE PROTECTION!!!If you make the pieces and take it to a welding shop, the shop charge should be a half hour for the welding. If you don't have drill press you may want to have the shop drill the holes.Get a piece of 1" thick marine aluminium alloy, draw the shape from the old one or the boom end (if you use the boom end you have to do the outside, then make a line inside with an appropriate spacer). Do this on a piece of wood first so you can make a pattern. It may take a couple of tries to get the pattern right. You will probably have to grind the final piece a bit to get it to fit.Then make the flat pieces that sit at 90 degrees to the end out of lighter aluminium, use the sheaves (pullys) from the old fitting if they're still good, copy the shapes and holes for sheave pins and mast attachment. Get it welded together, drill the holes, put it together and go sailing.If you can find or modify an existing part, it will be easier and maybe cheaper. If you're really stuck, you can make your own.Another option is to take the broken part to a fabricator/welder and have them do the project.