期指 歷史數據 ?

I do not know any free source.

tickdata.com have long historical HSI data for sale, you can also get them from the exchange.

2009-06-26 22:50:20 補充：
I was unable to send message to via Yahoo knowledge, so here is answer to your questions.

Yes, they are legit.

Yes, I bought a couple of months of data from them.

I cannot say if the data are accurate or not since I have not verify it.