I obtained a hammer spring for a .410 Miruko from Widners a few years ago and managed to install it. I tried to buy the tool they showed on their website for installing it, but they did not have one. the guy I talked to said he was thinking about making some more, but declined to make any promise. I made one that is like the tool you can buy to compress the top lever spring in a MX-8, it helped a bit.