After further thought, I think the manual may only show how to determine bolt and nut strength and torque of our standard bolts, etc. You probably won't find a part number for a bolt. You'll need to determine the grade, length, thread pitch, diameter.
However, since you have a loose bolt, a hardware store rep should be able to help you out. With a bolt in hand, you can determine the grade of the bolt using markings on the bolt head, generally. Bolt diameter and length, obviously, is easy to determine. Now, 'thread count' is generally used in SAE bolts and is determined how many threads/inch. We normally use metric bolts and those are measure using 'thread pitch'. That's best measured using a thread gauge if you have no info on the bolt. I believe you can even print offline a thread gauge, though one made of paper will not be as good as another material, but may still get the trick done if you want to attempt yourself or compare to what a hardware guys tells you. While at the hardware or equivalent store, the new and old bolt can be double checked using a nut that fits both of them as the final test before you leave. Dealerships may have info, too. That probably varies greatly.
This site,
https://www.boltdepot.com/Default.aspx, may help you determine it, as well.
I'm still surprised someone doesn't have more direct info. Maybe, everyone is still holidays recovering. Your hardware/bolt store, which most people have one around their town, still may be your best bet if you can't get a direct answer from someone else.