Online classes have honestly become a boom . Taking up  science just because there are no good teachers around you for commerce is not a reason good enough for forgoing your interest. I would like to share my personal experience with you . I did not take any coaching in class 11 and 12 for any subject except maths and that too in maths most of the syllabus I had to cover by self study only and I scored 97.25% aggregate in my boards.

I would suggest you take up online coaching and if you are not ready to pay the fees then you can take help of free classes on youtube . There are a number of teachers teaching on youtube for free. Believe me you'll ace your exams if you have confidence in yourself.

Even I am a CA student and honestly self study in class 11 and 12 made my concepts very strong and as a result I could  pass my CA foundation exam with a score of 308/400 . So I would suggest you to take up commerce and utilize the online resources for studying.

In case you cannot change your stream from science to commerce then focus on science completely. But honestly it makes no sense that you take up science even when you know that you want to do CA . So please think about it once . If you believe in yourself you can surely ace commerce exams with self study and online classes.

Thanks!