Well, w/o cheating or having the event Zoroark from August to breed it to other Pokemon, you can't. The way you were supposed to get it was by transferring over the Lock Capsule item from D/P/Pl/HG/SS that was supposed to be given away at an event, but the event never happened (think Azure Flute for comparison). You were then to take it to Mr. Lock in Opelucid City and he would unlock it and give you the TM. Tl;Dr It's impossible.
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