There is a company in India that makes a generic Mexitil. Here is their contact information...perhaps they can tell you how you can get it prescribed in your area:
You can also order it from Canada with a prescription. I don't know if that would be cheaper than what you're doing now: CanadaDrugs.com
It is against the law in the US to get a prescription for someone else. I did hear that mexiletine is going to be available in the UK again, but I don't have any information about pharmacies.
If you go to the search box at the top of the page and type in "India" you should be able to see all the people who have posted in the forum from your country. If they have made their email address public, there will be an icon at the bottom of the post for you to contact them.
As far as other medications, the generic names for them are acetazolamide, phenytoin, carbamazepine, flecainide, lamotrigene and quinine sulfate. While mexiletine seems to be the most effective, many people do well with one of the other medications.
For alternative medicine, you can use the amino acid L-Taurine (1000-2000 mg per day), licorice root extract, and capsaicin (hot sauce, red pepper flakes, or cayenne pepper). I don't use any medications, just the supplements and foods that decrease the myotonia.