Flippa and Empire Flippers ..
I heard this before and I think it's a reliable website where you can buy/sell business through Bitcoin.
They might accept Bitcoin as a payment method, but you would need to check their current policies or TOS.
In addition, these could be also good websites.
or join various communities and try to do things peer-to-peer.
A good choice, especially if have an escrow service that you can use.