I've never heard of this. :/ And anyway, the epsom salt is for the bloating, what you need is something to kill the infection causing the dropsy... I'm sorry I can't help you with other products. :( I'm not sure what else is available in your country for this problem.
One thing I can suggest is try to get metronidazole tablets from your vet, I did this because I couldn't find any of the pellets in my country.. Smash into a powder and stir into 1/4th cup of water.. It wont dissolve completely but stir for 4-5 minutes.. Add some FROZEN not freeze dried bloodworms and let them marinate in the medicine for 10 hours in a cool place. I kept mine in the fridge because they would spoil... Then feed these worms to the betta.. Just 2-3 of them once or twice a day. Make a new batch for every day although in the fridge you can get away with every other day.. :> good luck, I'm sorry i can't help you too much..