Dear Applicant,

You could go for b.ed in maths, as computer science is mainly for science students. The thing for B.ed courses are that, they are designed for BSC and BA students. So being b.com its gets abit tricky. Its is advisable if you do M.com first than go for b.ed ie. If you want to choose teaching as a career for commerce section. Otherwise you may not be able to teach in higher secondary. So if possible try to complete M.com. as you will get option for commerce related topic to study.

About admission, some college prefer to admit students through the process of entrance exams so check the college you wish to go and see if they are conducting an entrance exam. For this year the entrance are all done so you will have to apply  next year. But there are a few college that offer this course without entrance or else try distance learning.

Hope this helps. Best of luck.