I just built up a DIY rear light and was looking for the exact same parts. I found them at Digikey. I used a mini toggle switch with a silicone waterproof boot that screws on over the toggle. For the connector I found a Hirose one that is small and good quality. Here are some links:
You should also be able to find waterproof connectors for landscape lighting, though rather big. The proper size heatshrink can help. And, do a search for "sand sealed switch" I use these on my rail. Probably bigger than you want, but there is some options