The Professional is one of the three skins released as part of the Action Heroes (Volume 2) offer. It could be purchased as part of a item deal for a limited time in early June 2017.
The Professional could be purchased for $19.99 in the "Best Deal!" which included the Slaughter skin and either 50000 coins (Browser) or 1800 DNA (Mobile). It was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Note: The second volume of the Action Heroes offer was released again for a limited time in mid February 2019. The Best Deal was lowered to $9.99. Only the Slaughter skin and 1800 DNA were included items this time.