Why not simply buy a surplus Variac (voltage variable transformer) and do this, yourself? You wouldn't need a large one, a 5A unit (or higher current rated) would do just fine.
Readily available new, but also available less expensively used, from Fair Radio Sales (Lima, OH), http://www.fairradio.com
Just wire it up with a plug and a socket, plug in the equipment, and slowly crank up the voltage from "zero" to "full" over a period of a few minutes.
73 de Steve WB2WIK/6