The mower I have did come with a aluminium blade carrier, which had 3 blades, but the carrier was to badly damaged to repair. Their is a photo of the carrier on the forum. Cheers. Maurice
That's the problem with the alloy blade plate ,if you got one cast up it would cost more than what the mower is worth.
If you just want a working mower Maurice ,the easiest fix may be to use a second hand Victa 4 blade mulching plate.
I've used the Victa 4 blade mulching plate on utilities but have bent the top 4 flutes on the plate so they match the blade angle that way they are not pushing air downward any more.
Yep an Alloy blade plate doesn't seem like a good idea Mf.