Rick's right; you don't
add a grommet. So, to answer this question:
Which joysticks use a grommet for centering?
The most common sticks with a grommet-type centering system are:
Wico (note, some later Wico sticks used a spring instead of a grommet.)
Knockoff Wico Clone (often sold as "redball" or "leaf-type" joysticks. These suck.)
Midway: Pac-Man, Ms. Pac-Man Bosconian, Wizard of Wor etc.
Triggersticks: Tron, Xenophobe etc.
There are others, but those are the ones you're most likely to run into. I wouldn't reccomend a Triggerstick for regular gaming; only games that require such a stick. Can't reccoment the knockoffs either- the base is built wrong and the handles are loose in the grommet. Real Wico sticks are very nice, and so are Pac-Man type Midway sticks if you can get one in good condition. Sadly, neither the Wico or the Midway are made anymore, so you'll have to find one on ebay or from another collector.