I’m a real estate salesman in Wisconsin. I was fired. Do I still get my commissions?

There are two different issues here:
First, does the builder have to pay? That depends on the terms of the agreement, whether written or oral (unwritten) pursuant or according to which commissions were earned. It is legal to have an agreement where commissions are paid post-firing; it is also legal to have an agreement that  commissions are not paid after the person earning them is terminated. You need to determine what the agreement was--under what terms the work was done--in this case. Obviously, if there is anything in writing setting out the agreement in this regard, you follow its terms. If there is nothing in writing, look to past practice: what has this company done in the past, when someone was fired? Past practice can be used to determine the terms of an agreement. If no guidance from past practice, look to the industry norms: in your industry, are commissions generally paid after firing? If they are, then in the absence of anything more specific (e.g. an agreement) to the contrary, you should be paid, since in the absence of any stated policy to the contrary, a company would be presumed to do what its industry generally does, since that is the context in which it operates.
The second question is--who pays you? If you are paid by the broker who is in turn paid by the builder, you most likely have to be paid by the broker--and could sue the broker for the money--assuming that the agreement, past practice or industry norm is to pay commissions after firing. If you should be paid post-firing, it is the one who paid you, the broker, who should pay you now, and legally, that they were not paid by the builder would not be grounds to not pay you. Rather, the builder's failure to pay them would let them sue the builder for their money, but not being paid by your own client or customer does not let you refuse to pay your own employees or contractors.