They're fairly easy to find around here, but ... you usually have to ask for them. Check your lumber yard and local electrical supplies; they should have them.
They seem pricey at first, until you realize that, with 4 8' tubes, you're also getting two ballasts and cktry for them.
As far as bulbs go, well I see those all over the place including HD and Lowes, True Value, etc etc etc..
I use them in my shop; great light output and it spreads over a LARGE area too. I pull the mains wiring for the ballasts out and put two switches to a light fixture so I can have "decent" light with two bulbs, or "excellent" light with all 4 on. Mixed with a Halogen, they're perfect for finishing work - the dings & dangs stand out like a big orange box!
Be sure they're not too much light for you though. My Mother had eye problems so I put one in her little kitchen when she was alive. She loved it. But it's too bright for anyone else. Point is, if it's a small area with standard ceilings, leave room for one or two smaller fixtures for "just passing thru" use. Saves on 'tricity too. Ymmv
HTH,
Pop