gauge wheels more so the solid rubber gauge wheels *arghs* they can be expensive!
find a smaller size shaft, and then find a pipe / bushing per say. that fits over shaft, that will fit up into the deck.
find another pipe / bushings to make some washers, so you can properly adjust third party wheels.
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AGCO Parts Books
click on "guest" bottom right side
select massey ferguson from drop down
enter your model number
click search
click through to find your part number.
google your part number
ebay, amazon, harbor freight, tractor supply, grainger, northern tool, farm and fleet, farm king, and other ag / agriculture stores might have some gauge wheels. it be rare find, but perhaps menards, lowes, home depot. i know they sell some wheels but not sure about gauge wheels for finishing mower decks. if you have more of a mom and pop tractor store. not a big name brand dealer. but personal tractor shop, check them out, though i doubt they will spend time going through lots of books / part diagrams to find something, but they might have something already in stock you might be able to use.
generally around here there is a "lawn mower junk yard" per say, of some small repair shop with mowers all ligned up outside in the grass. they might have a beater deck to take gauge wheels off of.