rigrite.com shows it as
Keel-Mount Mast Step Ass'y w/ Adjuster: K-10674A-Adj:
Mast Step Assembly with Mast butt adjuster is as K-10674A, above, but with integral Ronstan Sealoc Adjuster and Adjuster anchor plate.
Seems like much money at $469 for the entire assembly but you might call them too because they seem to offer the a Steel plate and adjuster for $339.00 that’s not including the casting step that bolts to the plate.
Buy J24 Sparcraft Mast Step with Plate, sailing gear, sailboat parts, sails and running rigging at Vela Sailing Supply. Technical support, customer service and product information. Vela and sailing supplies.
vendors list shows Butch at MGB used to offer them