Why do you want to grow the most poisonous plant in the world? And why do you think we would know where to get seeds?
I don't think you should be trying to grow this plant, Harish.

This would be a difficult seed to buy in the UK, Harish; I would have thought that you might have more chance of obtaining it locally.
There are many reasons for growing A. ferox, Beattie, other than ornamenal. It has its uses in eastern medicine and for other purposes.

Crug Farm sell the plants, although I realise that this does not answer the question.....
However, from my experience of Aconitum, they seem to produce seed quite freely. So the answer may be to source a plant and collect your own seed over the coming season.
As Bulbaholic points out, the root is used a fair bit in "home" medicines on the sub-continent. By soaking it in cows urine it is supposed to lose a fair bit (if not all) of it's toxicity (not that I'm suggesting that any of us try). It's especially used for the treatment of throat infections, fevers and in the treatment of rheumatism.
It is used by homeopathic practitioners in the western world too.

Websites that specialize in herbal medicine may be a good place to check, Harish.

I am cultivating Aconitum ateox or A. ferox.
U can purchase this type of material from me.

Good to know, Ashutoshpokhriyal! Harish, you will probably want to use a private message to arrange that with him, to avoid publishing your private addresses, etc.