Generally you can find every updated lore on the champion's individual page found from here: http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/, but the website bugs out a lot and gives Riot problems when trying to update the lore from there, so it's not the most reliable. Here's some links for ya beyond Shadow and Fortune:
http://euw.leagueoflegends.com/en/featured/shurima/intro
http://na.leagueoflegends.com/en/site/mount-targon/story.html
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/fiora/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/gangplank/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/graves/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/hecarim/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/illaoi/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/jhin/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/kalista/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/karthus/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/kindred/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/missfortune/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/mordekaiser/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/poppy/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/shen/#champion-lore
http://gameinfo.euw.leagueoflegends.com/en/game-info/champions/thresh/#champion-lore
The Shurima site contains the lore for Azir, Xerath, Nasus, Renekton, Amumu, Sivir, Skarner, Rammus and Taliyah. The Targon site contains the lore for Leona, Diana, Pantheon, Aurelion Sol and Taric.
Right now Riot's current methods of presenting lore are laiden with problems from bugs to delays to all sorts of stuff, so the best place to look right now for all the current lore is the League wiki, which has everything cataloged in it. If you're ever in doubt, just go there and read up. That's the best source for all the lore as it stands right now.
I'll also elaborate on something here: Riot changed the game around September of 2014, which removed the Institue of War from the canon. This had the knock on effect of causing massive changes in the whole scope of the story of League, and the game and lore are now divorced so they aren't direct parallels, more like one informs the other. As such things from before that announcement, so from before September of 2014 vary in how canon they are. This goes from stuff in early 2014 which is almost certainly canon to stuff from 2010 and 2011, which should be viewed with extreme caution when examining what's actually proper lore now. The best mantra I can give you is that stuff from 2014 till now is just about 100% canon, stuff from 2013 is very likely to be canon barring some tweaks here and there (looking at you Maokai) and beyond that it gets muddier.
Right now Riot's fixing up the lore but it's a slow process, but we're getting there. Currently 29 champions are written to Riot's current standard, with Yorick, Ryze and Warwick all in line for updates soon, and some other champions such as Bard, Tahm Kench, Ekko and Rek'Sai also being worked on. Progress is being made but it's a slow process and we're not sure what champions beyond the ones I just mentioned are in line for immediate work soon, however this is the general framework for who's getting lore updates in terms of timescale:
- If X champion is being newly made and released in the game, they're getting updated lore.
- If X champion is being given a visual and gameplay update they're getting updated lore.
- If X champion is part of a large, region scope lore update such as Shurima and Mount Targon, they're getting updated lore.
So look out for those and you'll find updated lore in those.
