Reddit reviews Lee Full Blue (CTB), 20" x 24" Color Correcting Lighting Filter

As far as the diffusers go, you may get lucky at a local hardware store with some translucent hose or pipe or something plastic you can cut into sections. I took a look at the McMaster Carr catalog (which is a good place to go for basic materials), but they only have clear or opaque tubing.

You could also check to see if the color is really what you want in the room cheaply by purchasing a couple sheets of theatrical/cinema gel and covering your existing lighting fixture. You won't get the fluorescent tube look, but it would be some like $20 rather than the ~$100+ for the LEDs, driver, diffuser, etc. Something like Lee 201 would give a similar color wash to the room.