not wanting to "throw away" anything,after the change to the "New Models" they most likely used them for factory 'repairs' , sold some to various gun shops & gunsmiths back then....then around the time of the "lawsuits" ( mid 70's??) they stopped supplying "old model " parts.............I know we used to order them back then for 'repairs' .( they'd sell to 'smiths' but not the public..)
I'd bet they never MADE any more, after that, no need to.
Some of the other gun companies even stopped having "out side" repairs, especially "warranty work" and wanted all the warranty /repair work to come back to the factory...........(the 70's there was some serious 'litigations' in the gun industry) this is what 'spurned' the "writing" (billboard) warnings on the barrels..........
as for what Ale-8 mentions above, the "safety conversions" of the old ,models, basically just took out the "old model" works ( innards) and out in the safety conversion parts) and we've "heard
stories and tales of folks NOT getting their 'OM' parts back , but have NOT seen or had any NOT come back to us, or by anyone we know who has had it done..............