Zeiss Distagon 25 f2.8 ZF for 5d2

Hi,
Will somebody advise me where can I get a pre-owned 'Zeiss Distagon 25 f2.8 ZF', few sources in USA. I am in India.
My sister living in Atlanta is coming to India next month, she will pay and carry this for me.
I prefer this because I am basically in landscapes, (21 is too wide for me), I go for the 25 ZF, using an adapter. This is comparably cheaper, same time very good in sharpness and color rendition, I read. It is not available in India.
So, please advise me few shops who deal used lenses and reliable.
Thanks in advance,
Sunny Alan
sunnyalanoly@gmail.com