Are you looking for a Garden or entrance arbor? There are tons available wherever you live. Some you can install yourself (from a nursery) and others you can have a professional build and install them. There is a company in Georgia and Illinois named JakiJorg and they make a variety of arbors. Their product is unique because it is made with FULL dimensional posts. That means a 4x4 is truly 4x4 and a 5x5 is truly a 5x5. They also use copper, stainless or Miterless Wood post caps to protect and dress up the post tops. 

When looking for an arbor make sure it is installed deep enough in the ground to prevent "heaving". Also make sure the posts can sustain the weight from any plants you plan on supporting. If you have any questions and you live in Georgia or Illinois call JakiJorg to get the most for you money.