I see that this is a really old thread but wanted to chime in anyway
Broking can be a noun or an adjective. Acting as a broker is the adjective form (as in "broking company"), while the business of a broker is the noun form (as in "Acme Broking"). Broking is not a verb.
Broker is a noun and a verb. A rental broker, for example, is a noun denoting someone who links up renter and landlord for a commission, but doesn't own anything. Any intermediary is a broker. To act as a broker is "brokering". It means to act as an intermediary and applies to everything from brokering peace between nations to brokering the sale of a house.
A brokerage is the place where you do brokering work, or the business of brokering itself, or commission taken for acting as a broker.
So, in your case, brokerage.com or brokering.com would apply. Though grammatically incorrect in this context, broking is indeed being used by many in place of brokerage or brokering.