(Repeats to add missing word in headline) MADRID, March 17 (Reuters) - The head of Spain’s stock market supervisor said on Wednesday he expected around half a dozen of companies to make their debut in the Spanish market in 2021, which would set a record. “We could be speaking about half a dozen IPOs, which would be the highest since we have records at the commission,” Rodrigo Buenaventura, the head of Spain’s CNMV said on Wednesday.