You can measure your for steerer tube with a ruler, but I would bet a ham sandwich (with cheese and mustard) that it's a 1 1/8. Other sizes are FAR less common except some oversized steerers on high-end MTBs, etc.

Seriously, though.. just use a ruler to confirm.

Then, knock yourself out looking for the size and color you want online. At any given time there are thousands of stems on eBay.