I'm currently looking for books 6-11 from Katherine Applegate's Making Waves series. I already have books 1-5 but I can't find the rest. Can anyone tell me where I can get the remaining books? New, used, it doesn't matter. Thanks!

Check Amazon Amazon.com: Making Waves series aka Ocean City series.
Also have you tired Barnes and Noble?

To Blue Angel:
Yeah I checked Barnes and Noble. I can't find anything for them. I checked Amazon and it shows they are out of stock. I'm actually looking for these specific books: Secret, Attitude, Burn, Wild, Chill, and Last Splash. They are books 6-11 of Making Waves. I really want to find these! But thanks a lot for your help!

Here's another site you can try Katherine Applegate. It lists most if not all of her books and has a search to see if they're available for sale anywhere.