I ordered some 4mm replacements on November 13th and I recieved them today. I'm surprised it got here so fast considering how slow Canada Post can be. 

I needed them for a little game I bought back in 1997 called a Nano Baby. It's like the Tamagotchis. The rubber on the buttons were so worn that no matter how hard I pressed, the buttons wouldn't work. 

I had to trim up a bit of the plastic to get them to fit but other than that, it works like new! I'll admit that I was a bit skeptical at first but I can't believe how easy it was to install and especially how well it now works.

Thanks Ben!