The kit is essentially just a piece of rubber tubing. It channels the brake fluid away from the bleed nipple and into some sort of container. You should be abe to get it from any motor factors.
And yes, just the one caliper / drum at once. You need to get as little air in the system as possible, so its worth taking you time.
If you bleed them and they still feel spongy, it might be worth pumping the brake pedal a few times, and then opening the nipple, give it one more down stroke, and tighten the nipple back up. This can help push the last few air bubbles the end of the system where it can be bled.
Good luck mate