Well, it is possible in almost any of them, but depends at which price. If you asked me just a few months ago I would suggest Huobi or any other Chinese trading platform. They had extremely high liquidity that could easily provide 500 Bitcoins without much impact to the market. However, since February their government has banned Bitcoin withdrawals from the exchanges, so now they are not the best choice.
I’ll list a couple of trading platforms that could help you get the required amount.
But maybe a better choice would be so-called OTC exchanges (OTC = over the counter). OTC exchanges refer to companies or individual wiling to sell you Bitcoins directly and not through a regulated and automated trading platform.
OTC exchanges benefits
- High liquidity – OTC companies specialize in supplying high volumes of Bitcoin for large buyers such as institutional investors. This means you will be able to get your order fulfilled in full faster than on a traditional exchange most of the time.
- Fixed price – When you buy large amounts of Bitcoin on a public automated exchange you will probably see the price rise as your order is being executed. This is due to the fact that once you finish buying from the “cheap” sellers, you gradually move to the “expensive” sellers. This means you don’t have a fixed price for your purchase. When you use an OTC exchange you can negotiate a fixed price (e.g. “Bitstamp rate + 1%).
A few OTC exchanges:
- ItBit (for companies)
You can also try buying smaller amounts (up to 50BTC) on multiple regular exchanges in order not to disturb the market. Hope this answer helps.