My LeBlond came without any of the change gears when originally purchased
They guy who bought it made most of them, but had the 2 of them made at a shop here in town that specialized in gear hobbing. [They were an odd number of teeth that he didn't know how to cut].
Another source is of course the manufacturer. LeBlond wanted about triple for the gears that the local shop would make them for.
Sometime you can buy new old stock or parted out pieces. This gets risky, as you have to know how to properly measure gears' pressure angle and calculate circumferences for each Diametrical pitch or Module. Not rocket science, but takes a little skill and a Machinery's Handbook.
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A few words about purchasing used equipment: It can be heart rending to try to pick the 'perfect' or 'best' option. With some skill and information, you can more easily identify better options, but there is always a risk. Even with a new purchase there is a little risk, which can be helped by reading reviews or getting first hand information about the model you are buying.
The only way to get a good deal is to be able to quickly evaluate it and close the deal. Hesitating will ensure you will only have the leftovers to choose from.
I was the third guy to view a Bridgeport clone at a manufacturing facility. It was an 8X32, which was too small for them so it only saw about 50 hours of use. The other 2 guys hesitated for days. I paid the seller after 3 minutes of evaluation. I got an 8000$ mill for 2K$, essentially brand new.
Since the MSC isn't properly tooled (no 4 jaw, no steady rest, no face plate, no change gears) -- I'd pass on it unless you can satisfy 2 things: it is a smoking deal, and you are willing to spend a year getting parts for it. That's what it will take at a minimum. Expect that list to cost between 300$ and 1000$ to get the MSC lathe working satisfactorily.