Do you know how to buy and sell ADRs – american Depository Receipts / GDRs – Global Depository Receipts ?

Do Indian / Foreign brokers allow Indians to buy or sell ADRs / GDRs .. if so do you know the names or contact persons, and could you post them here or to my email address

for the sake of this post, please assume that I have the necessary foreign exchange

Thanks in advance
Regards
mani