You used to be able to buy replacement doors for the ST205 from Toyota dealers as I had to replace the drivers door on mine due to rust which was particularly bad along the lower seam. This is a known corrosion hot spot on the ST205.
As Sirius has already mentioned most of the secondhand parts are now posted by breakers on Facebook groups rather than eBay or web sites. You just have to do the leg work online if you want to track down panels. You also have to be careful with what is being offered as it is quite common to find breakers simply chopping through the rubber boot wiring loom between the door frame and the door itself. They also tend to strip the glass, motors, locks and all the other stuff out of the doors.
I'd suggest giving Paul Pridham at TCB Parts (
http://www.tcbparts.co.uk/) a call on 01579 383879 as he is very knowledgeable regarding what parts are still available from Toyota and also may have stock, or know of, secondhand panels.