I wouldn't do it with custom hardware (at least not directly)
Maybe the economy or marketplace would be a good place to start looking.
Read up on "dark pools" Some trading houses have them but I think it costs more in commission.
If you want to go straight market... Mt. Gox would love to you have your business and since you are looking to go to BTC, they still have the most liquidity. I would wait for a big dump in the price personally... some whale(s) has been pumping the price up the last week, and I think if the general market doesn't jump in, they are going to start dumping. You could buy 10K btc easy.
If you seriously are looking to buy 10,000 btc, some other thoughts would be to contact the large BTC only asic vendors as I am sure they are flush with BTC right now and would probably like to talk to you. If you don't know who those vendors are... you probably shouldn't be buying 10000 BTC.
There... see... I was able to spin this into a custom hardware thing after all.