I could find many sellers for the bitmain chip. I asked for a bulk amount, which was about $8. I'm guessing just a few chips will be more expensive per unit, or they might want a minimum order of some amount (I hope no higher than 10).
As for pinout diagrams, it seems they would be your only real problem, shame I can't help you with that. I am pretty sure you can buy these chips though. At least for the S9. I don't know about the S7.
-edit-
Ah, it's an S7. I would have looked up for you on alibaba, but I can't find the specific chip? Ah, found it. It's a BM1385. Yes, one seller does seem to have it for sale.
https://www.alibaba.com/product-detail/Miner-ASIC-Chips-BM1382-BM1385_60707278004.htmlTry contacting them. Hope it's any help. Good luck. Would help you more as barmitzfit said with the pinout chart even if you can buy the chips it seems there will be more problems.
There seems to be many more retailers for the S9 chip than the S7
The only reason I asked for a pinout was to determine if they were a scam or not. I mean, how can a company that sells these chips not have any technical information? I don't think the ASICs on alibaba are real, I see a lot of threads on here discussing how people can create their own SHA256 ASIC and most of the answers come back saying it's impossible (The equipment used to make them is in the millions).
edit: I mean this from my own expierence, I contacted a few of these suppliers and they never answered after I asked for any technical documents