Where can I buy Moc in GTA 5?

Excuse me, could you please clarify for me where exactly one might be able to acquire Moc within the virtual world of GTA 5? I've been searching high and low for this particular item but have yet to find a definitive answer. Is there a specific in-game store, a mission that rewards it, or perhaps a certain location where it can be found? Any guidance you can provide would be greatly appreciated.