Generally, strikers are sold as complete units. Additionally, they don't wear out very often, I replaced my first one at 10K, took a look at it and realized it was fine so I ran the next one another 40K, I changed it out because the next one was the "new and improved, seriously shiny" one. The 40K striker was fine too. What issues are you having that's convinced you to replace your striker spring?
Murray Charlton Enterprises is the Canadian Warranty centre for S&W, or if you need a bunch of stuff, you can order though Brownells.