Unavailable Skins

With all the new people joining and more people spending money on the game, I know there are lots of people who would love a shot at some unavailable skins that may have been available for purchase at a previous time.

No, I'm not talking about Grey Warwick or Black Alistar or the likes, but rather skins such as Riot Squad Singed and Riot K9 Nasus. I know for a fact I would spend the money to get those skins even though I already own Infernal Nasus (1820 RP). I would never dream of buying off of a third party site but then again I never had a chance at the skins.

Other than PAX, LCS Live Events, or other events where codes are given out or purchased, are there ways to get these skins since they aren't available in game? I can understand that there are skins that should never be made re-available for the sakes of keeping them rare, but will there be new skins of that sort for the new AND the old players to feel like they are getting a rare skin that won't just be available the same time next year (ie. Legacy "Holiday" Skins)

At Pax East (which I did not attend) recently the Riot Kayle skins were available. Is there some reason the Riot Kayle skin codes are still given out and are not expired like the similar Riot Blitzcrank, Riot K9 Nasus, Riot Squad Singed, and Riot (squad?) Graves?

I often watch LCS and PTL on twitch and I know they've given out codes for things there but I think it's common knowledge bots often snag those codes before any person could. If not, props to them for being able to type that fast.

On a seperate note, Archduke Nasus DEE CANE

PS. I don't post on the boards much, is this the right board for this, or would there be a better place for this thread?