Seems to me you have four choices:
 
1. Online practice for free (I googled “online business writing courses for freeâ€). There are many courses available, with the only drawback being you will not deal directly with a “realâ€ person or an instructor.

2. Online courses with instructors: You could look at Phoenix, Strayer, the multitude of other online universities, and any college near you as most offer online courses now.

3. On-campus courses at local institutions. You could sign up for a business English course, depending on your prior education. I believe you could even audit one, which means you get the instruction but not the credit.

4. Local tutors. Check Craig’s List and similar services for one-on-one tutoring.

I suggest you start with the free online stuff, see what kind of feedback you get, and then decide if you want more communications with an instructor, either online or on-campus.

I hope these thoughts/suggestions are helpful. 

Jackson