it really depends. like @AkiraCondry i have my 'ticketmaster' and 'live nation' accounts set up to alert me if one of my groups comes though the U.S. and now I also follow SIVA GROUP on insta b/c they work with korean musicians mostly r&b, hip-hop, and rappers (they're the ones that brought Epik High over) *best concert ever!* Soompi and Allkpop usually has info when groups have U.S. tours too. But really for me it's been pure dumb luck to be on the apps when the tickets or tour was announced and thats how i got mine LOL. Infinite hasn't posted all their tour dates yet so keep an eye out there's still hope! *oh also the group's official youtube page is a great source of info, i know looking in the comments is sometimes cringe worthy but usually someone in the fandom has answers. Sorry for the long post but I hope that helps a little!!
I buy my tickets on 'ticketmaster', so my account is set up so it sends me notifications when my favorite artist are coming near me.
I don't know about Infinite.... I looked it up but there were no dates. So either that means they weren't released yet or there are none.
I'll ask around to see if anyone knows, for sure :)
LOL i know right? but whatever works i'm not complaining. its how I got VIP M&G tickets for Epik High, floor seats for BIG BANG in October, and really close seats for both 2pm and VIXX concerts. good luck!