Looks like you have a 3 blade maxprop...
This link should help you decide what you think you need...and you can probably get it cheaper from somewhere else.
I'm confused by what you mean by the "plate" zinc....are you talking about the rectangular plate on the side of the rudder?..if so that's not a zinc, its the ground plate for the SSB radio.
If your rudder zincs are fine, but the prop zinc isn't you may have a bonding issue...the rudder zincs should be decaying....in fact you shouldn't need the prop zinc if your bonding system is all good.
Elyse SM437 Musket Cove, Fiji