Welcome to the forum. It would help in answering your future inquiries to know what model tractor you have, and even what state you are in.
As a partial answer to your question, the attachment plates are unique to Power Trac, and even then come in 4 or 5 sizes depending on the specific model.
They do sell these plates, and most any welder can cut off the unnessesary skid steer brackets and weld on the appropriate PT plate. Sometimes you can mount a PT plate and still keep the original mount if you would still have a use for it.
Keep in mind the total weight of the attachment as many intended for skid steers are fairly heavy. Also, note that the lift arm/attachment plate geometry on PTs is not like most skid steers (or CUTs for that matter) in that to get any bucket curl up when down on the ground the plate should be mounted at about a 30 degree forward angle from vertical. If you study the pictures of the various PT attachments, you will see that most are set up this way for this reason. Most SS attachments are designed to have adequate curl with a vertical attachment plate.
If you buy a new screening bucket from the manufacturer, you can often either get it without any mounting brackets or have PT send a plate for your model machine directly to them and they can weld it on and paint it before shipping to you. Be sure to discuss the mounting angle issue.
You may get by with less than 30 degres for your machine and application, just check and measure the geometry on your machine.