What look/shape are you wanting? How big is the pot?

They'll happily grow up anything at all--wood, iron, bamboo sticks, obelisks, tomato cages, whatever. I've used store bought (wood and iron trellises and obelisks in various pots) .... one year just got some bamboo sticks, and tied them at the top, in a triangular shape. Another year, I used an old metal garden rake (reinforced the base).

It's easy to make an obelisk out of branches, if you like a rustic look. HD and Lowe's sell metal ones that are fairly inexpensive, too.