Where do I buy a Copper deghra for making biryani

[Anita]

Hi Guys, I live in London and am missing my regular fix of hyderabadi biryani. My mother is going to Hyderabad in November and I was wonder if any of you can tell me where she can buy a deghra to make biryani in. I remember we used to get the copper ones with a tin coating in begum bazaar (I think). Not sure what size I need to cook for 6-8 people. The website says it should be 1/4 empty for the steam to do its job successfully. Any pointers will be very much appreciated.