There's nothing you can do on them, but the award pages are:
https://store.steampowered.com/SteamAwards/2017/
https://store.steampowered.com/SteamAwards/2018/
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Nothing you can do, but Steam Holiday Auction 2014: https://steamcommunity.com/auction/
Edit:
Found another; Steam Summer Event 2015: https://steamcommunity.com/minigame/
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Just saw: https://www.steamgifts.com/discussion/9GYuN/fixed-steam-sale-rewards-bug
Wasn't in time... (R.I.P pig in blanket) but I thought there should be many more sides up and maybe, maybe someone missed one of those.
I begin, maybe some dosnt help, maybe some do.
springcleaning: https://store.steampowered.com/springcleaning (Maybe you can still do missions)
salien: https://steamcommunity.com/saliengame/play
Steam awards 2017: https://store.steampowered.com/SteamAwards/2017/
Steam awards 2018: https://store.steampowered.com/SteamAwards/2018/
Steam Holiday Auction 2014: https://steamcommunity.com/auction/
Steam Summer Event 2015: https://steamcommunity.com/minigame/
Will EDIT every time someone gives me a new site.
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