Chirantan,
I would recommend that you apply for a B1/B2 Tourist Visa in order to appear in the Step 2 CK examination. The best way to do this is by getting in touch with a doctor over e-mail who is faculty at a teaching hospital (such as Johns Hopkins, Mayo University, etc) and arrange to take part in a short-term observership or research elective as an international medical student.
The school should then send you a letter confirming your elective which you can take to the US Embassy in India and it should assist you greatly in getting a tourist visa.
Once you are in the US, not only will you gain some good experience, but you can also sit for the Step 2 CK exam.
In regards to which residencies are offered to IMGs, basically almost everything is available but for an IMG, it is more competitive to get fields such as surgery, radiology, dermatology. However, there are many exceptions and the things which matter in making you competitive are:
USMLE scores, US clinical experience, research experience, and letters of recommendation.
If you do a research elective in the US while you are there to give your Step 2 CK exam, you will be getting research experience, and a letter of recommendation which should definitely help your residency application later on.
BTW, is your internship in India required or optional?