Where can I find "Metroid", the "Airwing" and "the master sword" items?

Master Sword & Arwing: They are sold as Spotlight Items from Tom Nook's Shop. There is a glitch that will prevent any spotlight items from showing up at Tom Nook's Shop. If you are the only person in your house, the glitch will occur. To fix it, create another character to move in with you. If you do not want to, the only other way to obtain them is through shooting stars (press A when you see one). If you have more than 1 person in your house, you are only having bad luck.

Metroid: (in case you have never met Gulliver, you should read the following. If you have met Gulliver, read the last 2 sentences) Occasionally, from Monday to Friday, you might see a U.F.O. fly by your town (it appears if the last digit on the clock is 3 or 7. For example, if you walk around and it's 5:27, Gulliver will fly by your town) If you are carrying a slingshot, you can shoot him down (similair to presents floating on balloons, you have to be on the northern side of your town to shoot him down). However, his U.F.O. can fly faster than a present floating on a balloon, so he will be harder to shoot down. Once you shoot him down, he will pass out. Talk to him until he awakens from his coma. He will ask you to repair his U.F.O. by giving him the pieces that have came off of his UFO when he crashed. After giving him the parts (there are 5 of them), he will give you a gift. It will not always be a Metroid, and if it isn't, you will have to wait another few weeks to find him, shoot him down, repair his UFO, and so on, until you get the Metroid.