>>5483449They're mostly sold on Japanese websites; Amiami, HLJ, Hobbysearch, etc. You can buy them from Amazon for assrape (moreso than normal) prices, or you can try to use sites like Ekia Hobby or BBTS.
There are currently seven MoMos available, though many of the earlier releases such as Ingenue have sold out and can be bought secondhand from sites like Mandarake.
MoMos are pre-built and assembled modular figures. They don't need to be painted or anything; though if you wished to do so there's nothing stopping you of course. They're intended to have parts that can easily be swapped with each other.
Be careful as MoMos have earned OE some flak for what many see as poor QC and broken promises, etc. Zwei earlier appears on her box as having a sheen/coat which isn't present on the actual model, Hi-Riridine and Chocolatte here were presented as looking like they had gunmetal colors but they were mostly flat gray. If you're on the fence about buying one, make use of your best judgement.