HNY Jim,
Play around with the Search option on the top of this page. There are shoes being made. (But I must say I disagree completely with the alloy.) I've seen very rare mentions of alloys having to be the same. It is my opinion that the shoe and the shaft MUST be the same alloy. Even so you have to trust the supplier, who I would actually ask for the alloy percentages even where they originate.

Personally I chose what I consider one of the purest Bronzes available, a real bronze, not a brass masquerading as a bronze they sell to the pleasure boat crowd. Everdur 655. Almost pure copper + a pinch of silicon. Manganese bronze is nearly 40% zinc. In the iffy environment of salt water, hot marinas and no positive way to protect metal, that has too much of a spread. For me. It's a fine strong alloy for stem fittings, chain plates and the like.

I would mate the M. bronze shoe with the same in rod for the shaft. But then what will you use to hold the rudder planks? Could thread smaller rod to make the 'bolts.' Could be done avoiding ubiquitous silicon fasteners available almost everywhere. Ah, yer thru hulls are another unrelated brass called bronze. My Everdur cost like gold. Don't think M.B is cheaper, don't know, tho.