I used the original bolt from the factory pulley. You can cut off the front of the original pulley with a cutoff wheel to liberate the bolt, and then use the pulley available at the part stores. If you have the right equipment, you can press the old bearing out from the back, and press in a new bearing with the bolt around it. Cause basically only the bearing is bad, and is only about $2 front sources online or supply stores.
I can dig up the part number for just the bearing if you want to go that route. It is also the same bearing for the lower idler pulley (with A/C), which is easier to swap out since that pulley is not closed on the front.
Or like I said you can cut out the front of the original pulley to get the bolt, and get one the in the first picture from RockAuto (the Cheapest), or pay a little more at local part stores.