there are some around, the issue is accuracy, when is a -6 a real -6? Some book could be 6.5 another might be 5.5. The DB is only going to spit out what it has in it. Garbage in, garbage out. It is more notoriously inaccurate around the 3.
A lot of guys strip/mine their own stuff these days. But that still doesnt mean it is completely accurate.
A lot of places not only close at different numbers, you also have spread moves and vig changes to contend with. Add that to teaser protect numbers and it gets very complicated unless you use the same criteria for every thing you do.
As far as your question, and according to a generic DB.
Since 2000 there have been 796 games lined between 6 and 8. 24 won by 6, with 5 of those being called pushes; 46 won by 7, with 9 of those being called pushes; 16 won by 8 with 2 of those being called pushes.
So in that range of spreads, you have 86 of 796 that fall within a 'decent' proximity of the posted number(s). Of those, at least according to this DB 16 of them landed on the number they used as the number for that game.
Now I am sure if you looked at every single game where the lines were available at those numbers you would obviously find more games, whether or not the results stayed the same is another question. I am positive you could have found numbers that would not have pushed, and I am positive you would have found numbers that would turn loses into pushes, maybe even wins. So even with using a range you have to be aware of the variety of lines you can find as well as expect to get.
Also in some cases just because you see a line it also doesnt make it equal. Someone could cite -6 for a line somewhere and it might show on a history, but if the line ends up being 7.5 everywhere you can assume the limit on that game was so tiny it wasnt worth noting, or it could have been labeled a 'bad line' and any bets made on it voided. Even though it was offered in good faith.
You always have to be aware of the REALITY of sports betting when looking at results, especially in results spit out by a search.
But everyone loves numbers and they do give some insight sometimes. But mostly in the though process of books and betters, especially if you see a pattern develop in certain spreads.