The problems are pressing on many users. There are not replacement part sold in global market yet. But I think the retailers will start to sell the HTC ONE M8 camera lens in the near future. You can keep eyes on witrigs.com.
What's color of your iPhone5s? You can get iPhone 5s top and bottom back glass and Camera Lens at here. You have to teardown the iPhone 5s for replacing the rear glass. If you pry rear glass up instead of disassembly, it is easy to break the back cover.
The core part is the motherboard of iPod Touch 4, which is hard to get. I think there is not a original and brand new motherboard in the market. So you have to get a old one in a hand market. The replacement part is easy to get. The ifixit iPod tough 4 teardown will give you a hand to build it. You can get iPod Touch 4th Replacement Parts at ifixit store or witrigs. You need LCD with digitizer and frame, back cover, EMI shield, headphone jack, battery, rear facing camera, Front Camera Fastening Piece, back facing camera, speaker, WIFI Flex Cable, Power and Volume Button Circuit.
You can get a new Nexus 5 LCD screen assemblyand try to replace it by yourself. The LCD, digitize and frame are glued together tightly. It is very easy to break one part when you replace other part. So you need to replace the whole assembly.