I'm happy to help you in your preparation. While there are a few different types of online cases, and we need to define which one it is (online test, written case, take-home case, etc) I've helped candidates with all of the above!
In regards to OC&C specifically, you may be hard pressed to find coaches who specifically specialize in OC&C interviews. However, the preparation across strategy companies that conduct fit+case style interviews is 95% the same!
You really don't have to worry too much about OC&C specifically as much as you may think. That being said, you will want to focus more on the areas the OC&C is known for (PE, M&A, CPG, TMT, Retail, etc)...any coach with sufficient time working in MBB would be comfortable with most any industry/service