Try your town dump, goodwill, free cycle
If you get stuck I can sell you one that is already modified and rewired, and all you have to do is hook up the diodes and a cap, if you want to adjust the voltage that can be done using a light dimmer I use a magnetic light dimmer tied into the primary of the microwave transformer this supply can also be used as a welder, and a car battery charger, and even start the car with it, so what you will have is something you would never want to throw away you can also use it so it only puts out between 1.5 to 3.5 volts @ 140 amps way more then you could ever need
Try and buy a supply that can do that, and expect to pay about $5,000 to $8,000 there just is not much call for very low voltage high current supplies
Gary