That's a beautiful boat. I think the Tempest is one of Oday's best looking boats, and a great sailer too. As for the items you are looking for:
you can look for used sails on line. There are a bunch of brokers: usedsails.com, secondhandsails.com, etc. According to the I Heart Odays website, the measurements for a Tempest are I: 26'6", J: 8'5", P: 23', E: 10'. Even if you don't find a used Tempest main, you are sure to find something that is close enough that can be modified by a local sailmaker. But I suggest you measure your own rig before you plunk down any money; the measurements quoted on line are not universally correct.
I'm afraid you are going to find yourself SOL looking for used interior cushions. There aren't a whole lot of Tempests left floating around, and it seems to me highly unlikely that you will find someone willing to sell the cushions out of one. And no one sells replacement cushions for defunct models. There are only two ways to get new cushions for a boat like yours: pay someone to custom make them, or custom make them yourself. I am going to predict that it will cost more than what you paid for the boat to have someone make them for you.
Good luck, and send us pictures as you go!