Good remaster from the 2011 The Elder Scrolls V:Skyrim. But if you want to buy the original skyrim to mod the crap out of it (because the original game comes with so many mods that isn't available in the Skyrim Special Edition), then here's a link to the original Skyrim for you. Apparently if you search the original skyrim, it will not show up for a reason.

EDIT: You can find all the DLCs here

http://store.steampowered.com/app/72850/The_Elder_Scrolls_V_Skyrim/

https://store.steampowered.com/app/220760/The_Elder_Scrolls_V_Skyrim__Hearthfire/

https://store.steampowered.com/app/226880/The_Elder_Scrolls_V_Skyrim__Dragonborn/

https://store.steampowered.com/app/211720/The_Elder_Scrolls_V_Skyrim__Dawnguard/

https://store.steampowered.com/app/202485/Skyrim_High_Resolution_Texture_Pack_Free_DLC/