If it says: "Umin 18V AC / Imax 250mA, 50/60 HZ," all you need is a wall-wart transformer that can output 18V AC at a minimum of 250mA. You can buy such from Radio Shack or any of a number of mail-order houses like Mouser or PartsExpress. However, considering your professed ignorance, the problem will be getting the right connector set up.
BTW, the Thorens likes more than 250mA, if available.
BTW, the Thorens likes more than 250mA, if available.