tlm: I'd suggest you to consider the SS445E/U from Ebay vendor "wolfsbigbadgarage" for ca. 36 bucks. Just like your/your son's current TR475U, the SS445E/U also is a "renamed" AT102P family model, but equivalent to the AT122EP instead of just to the AT112EP. So those 36 bucks would buy you/your son a new old stock, original ATN122EP plus a spare AT102P family body (in case the one from the TR475U wouldn't work anymore - which hardly ever happens with AT MM bodies, though...) plus a complete set of accessories, also including a needle guard/protector. Given that the most recent incarnation of the halfinch-mount version of the AT122EP, the VM530EN, already is roundabout 180 bucks new, those 36 Dollars for the SS445E/U practically are a steal - so that I'd actually suggest you to grab two exemplars.
That being said, another attractive option from the same vendor would be the ATU4040EP (= renamed AT316EP) for ca. 35 bucks, which would even be slightly better than the SS445E/U in terms of needle quality due to sporting a diamond with a rectangular instead of just a round shank, so that it's got a slight advantage in terms of equivalent tip mass (ETM). However, disadvantages of the ATU4040EP compared to the TR475U and SS445E/U would be, that the AT3472P/301P family, which it belongs to, doesn't have a directly needle-compatible halfinch-mount counterpart, as well as that the choice of higher quality original AT needles for this family was a lot more limited. Hence the current upgrade path with the ATU4040EP would end at a 3rd party, bonded Shibata on straight non-anodised alu cantilever, whereas on the AT102P family bodies of the TR475U and SS445E/U you could still use any original "wider AT120E family" needle up to the current VMN60SLC...
Greetings from Munich!
Manfred / lini