We’re based in Seattle. We’ve not found off the shelf zincs to fit so we have had to get them custom made.
Look for a zinc plate (eg Fisheries Supply, 12″ x 1″ thick x 6″ wide). We had a shipwright cut these into bars 1.75″ wide to fit the width of the slots. To fit the bolts, have them drill one hole and one slot about 1″ long to make the fit easier. We also replaced the original bolts with longer ones to accept thicker zincs. BTW, shipwrights here charge way too much for shop time!
Note, we are also able to use a thicker zinc because we counter sink the bolt holes in the zinc to allow us to get the bolts and lock nuts on, and still have the thick plates. I wish we had put longer bolts in to avoid the need for the counter sink.
Hard to believe your plate lasted 6 years. Ours, made with thicker plate, last about 2 years. Our hull #126, can only take a 12″ long zinc, not 15″.
Good luck,
Van