You always report income, whether or not it is reported on 1099s.

I'm guessing the S Corporation is not in the business of selling its own stock, so it has no requirement to issue a 1099-B.

Basis in S Corp stock only begins with the purchase of the stock. You need to add all items of income and gain, subtract all items of loss, separately stated deductions, and distributions for all years to get the basis at the time of sale.

Additional complications ensue if there were prior sales or if the shareholder loaned the S Corp money.