Bulb
You can get the bulb at just about any hardware store. They're 125V, 15w and usually marked as a Vacuum Cleaner or "Appliance" bulb. It'll have a brass barrel around it with 2 contacts on the end. They're common as dirt.
That bag shouldn't be hard when the machine is running. If it's hard, it's because the pores are clogged and it's not working as well as it should. You can hand wash it in warm water, although I've successfully washed them in the washer on the delicate cycle. I don't have a modern washer, so I'm sure that has a LOT to do with my success too. No "Shredmore" for me, thanks!
If you wash the bag, be sure to use fabric softener in the final rinse, or when you wash it with clear water in the sink (depending on how you're washing it). It'll make the fabric softer and it will actually filter better. If the bag is washed well, you won't see dust escape when you thump it while the machine is running.