reacz - Portal Textures - http://gamebanana.com/textures/2868
KeNnY1337 - Skybox - http://gamebanana.com/textures/3283
A Boojum Shark - Mapping Resource Pack - https://tf2maps.net/threads/ultimate-mapping-resource-pack.4674/
Alternate download link: https://mega.nz/#!L1wiSTbS!0TJ73LnUzspnBLMa_J3V8kSEVxCaUjhscWQ1I5Ymk4I
I would attach images but it seems that the site is throwing an error when I try, so here's an imgur album: http://imgur.com/a/CY3d2
Note: The platforms have a 50/50 chance of appearing on round start.