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.html
Try 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