How can we receive PAX skins? Will you give an event for that?

http://www.paxsite.com/

PAX is (multiple) real world expo events, that cost real money to attend, and of course you need to physically be there. Theres attendees from a whole range of gaming and similar companies, potentially including league. PAX east and PAX west are probably your best bets for ones that will have a league presence (kepe an eye on the league site itself for new regarding that).

Theres no guarantee that riot being at a pax event will mean they're giving out PAX skins though, unless announced as part of the event. They've previously given out riot ward skins and a few other 'regular' skins instead of pax ones. In fact there is a guarantee that they won't give out the pax skins you're familiar with (Pax sivir/TF/Jax), since those are limited skins. However, the recent neo pax sivir means they might do similar for Jax/TF in the future, so while you can't get Pax TF or Pax Jax, there may be hope for neo pax TF or neo pax Jax to become a thing.