Stevens, who coached Tottenham's Dutch playmaker Van der Vaart while in charge of Hamburg, has indicated he would like to be reunited with the 29-year-old as well as acquiring the services of Chelsea forward Kalou, once his contract runs out at the end of June.
Van der Vaart's agent Robert Geerlings recently confirmed that the Bundlesliga outfit were interested in bringing him to Gelsenkirchen.
But the former Real Madrid star played down speculation surrounding his future, insisting he is happy at Spurs, despite revealing a desire to play in the Italian Serie A at some point in his career.
"His qualities are unprecedented," Stevens said. "I would love to work with him again. We have contacts with his agent. Every day I speak to Horst Heldt [Schalke's general manager] on the phone about our plans.
"There are rumours circulating that Rafael would return to Germany. But I have not heard from his mouth. I have not spoken with him and we'll have to see after Euro 2012 .
"He has a contract so we will have to pay a ransom. If Rafa really wants it, he is welcome.
"If that opportunity arises, and he looks forward to it, let him come."
And, on the subject of Ivory Coast international Kalou, 26, Stevens confirmed his admiration but also revealed Liverpool were battling for his signature.
"Kalou is a Bosman player this summer," he said.
"It's obvious; there are many other clubs keen on him. Liverpool for example. But I know for sure he wants to move away from England. This could be our chance!"