If your spring snapped when you tried to bend it, I'd say there's a good chance this remedy has been tried before, and it just couldn't take any more bending.
MidwayUSA looks to have the spring in stock, not sure about the rivet.
Smith & Wesson Trigger Play Spring S&W 3953TSW - MPN: 234230000

...aaaand here's the rivet !!!!
Smith & Wesson Trigger Play Spring Rivet S&W 3953TSW - MPN: 068770000


I merely googled the parts, and then posted what came up, but now looking closer, I'm not 100% sure these are correct parts for the 4506, though they look identical. So, double-check, first.