I get almost all my stuff from covers33. They do a Japanese style liner or a lined paper in black or white. Depends how many you have to do. Top ones are MoFi, I bought a bunch once but don't really see the advantage over the basic Japanese style.
Seconding Airhead on covers33 - they've been my go to for a long time. I keep a stack of black and white inners for anything that comes without them / some of my old records that are getting a bit tattered. I also use their outer sleaves and have been happy with them too.
Anyone recommend a decent inner sleeve?
As usual I can spend a lot or a little and I don't know why.