Due to its abundance, oak was used by everyone. When the rich began to look for a way to advertise their wealth, they used oak to make elaborate pieces of furniture. Lighter wood took oak's place in the 1600s, then it became popular again in the Arts and Crafts period in beginning of the 20th century. Oak is still used today to create furniture for the dining room and so much more.
For oak tables made of heavy oak or in the Arts and Crafts period, you will have a good chance of finding them at an antique store. There, the tables will feature hand joinery and dovetails, and can be the plain, roughly-hewn tables of long ago, the ornate tables of the middle ages, simple lines of Gustav Stickley. The tables will vary in price as well as condition. Examine the table carefully before bringing it home.
If you prefer to make your own oak tables and chairs, you can do so from solid oak. These can be in the form of lumber from Lawson's Timber which features reclaimed lumber, UK Oak that will cut oak boards to your specification, and UK Timber. With these boards, you can use dining table designs of your own or from books like Making Authentic Shaker Furniture which includes designs and directions in the book. These tables can be made so well that they could last hundreds of years, just like the solid oak dining tables of old.
If you prefer to buy your oak dining room table, then there are furniture stores that sell them in a multitude of styles ranging from the traditional to contemporary. Companies like Oak Dining Tables Sets, Oak Furniture Land, and Berry Design will have many oak dining tables in stock from which to choose. The prices will vary as well as the quality with which these tables have been constructed. You may even be able to buy a dining table and chairs set or just the table itself. The furniture will have a number of different finishes, which will make it easier to find the table that best matched the décor of your house.