I'm fairly new to sports betting, so forgive me if I come across as ignorant.

For teams favored by 6 to 8, I'm trying to calculate the probability of them actually winning by 6, 7, or 8. Where could I find this info? I'm looking for something along the lines of, "there have been 2000 NFL games with a team favored between 6 and 8, and in 100 of those games the favorite won by 6, 7, or 8." I hear stats like this all the time, but I'm not sure where these searchable databases are located.