OpenQuartz - A free (as in freedom and beer) Game Files replacement
If you're dumb enough to give nu-id Bethesda Microsoft you're money, you could technically buy it on Steam.
All of the low hanging fruit places to grab pak0 and pak1 disappeared. Oh well. Buy it on GOG when it's on sale, I guess.
Your sourceport executable should be in the same folder as your id1 folder, as pictured.
Consider setting 2D Filter Mode under Options > Texture Options to "Nearest." It may already be set but not actually working properly: change it and change it back. This will make your textures look crisp instead of blurry.
Also consider setting cl_truelightning 1 in the console, which can be opened by hitting Grave/Tidle (`/~) in most places, or Escape in the menu. This setting aligns the lightning gun's stream so that it doesn't lag behind you while moving.
And last, but not least, have some fun with Ranger!
If you're looking for something new to play on, why not try a homemade kenya map? Put it in id/maps/ inside your Quake folder!