Average player doesn't need to worry about super specific manufacturing points like stick box placement/motherboard, shield drop angles, etc. Just focus on having a working controller that fits your preference (some people prefer sticks with a little loose wear, others prefer as new as possible)
If you need a new GC controller, best bet is to carefully check ebay, craiglist, goodwill, similar things. Assuming you want an older GC controller (Purple, Platinum, Orange, etc), you will probably have to settle for a used controller. Not always easy to confirm condition without testing it in person so some caution with online options needed. Otherwise, just pick up a Smash 4 Logo controller and use that