I studied for CASC by regularly practicing stations with friends from a book called Pass The CASC (https://www.amazon.co.uk/gp/aw/d/1498707890/ref=mp_s_a_1_1?ie=UTF8&qid=1488701670&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=casc&dpPl=1&dpID=41U%2BxOB4VsL&ref=plSrch). It provides brief scenarios and an excellent marking scheme for each. I found getting used to 7 and 10 minutes helpful and also getting comfortable with making mistakes infront of others!
I also used the SPMM videos but I found the associated handouts a bit too much to read through. As its a practical exam I felt practicing clinical skills was key. If you've passed A and B the knowledge is there, its just a case of conveying it to a patient in a simplistic way.
I didnt go on any courses but we did a practice CASC here in Edinburgh. I wouldn't recommend the Pass the CASC book by Dr Moodliar, I found it to be a bit overinclusive in terms of their approaches to stations and I'm sorry to say that it was poorly written!
Practice. Practice. Practice. Keep calm and you'll be fine.
Happy to speak further with anyone if it'd be helpful. Good luck!