You should be able to use any USB charger. If you have a phone that charges by a USB charger, you can probably use that.
A lot of their portable speakers and headphones no longer come with the charger itself, just the USB cable. Not sure why, but I think it's about reducing waste. They no longer have to supply all the different plugs that most people just throw out, and I know I already have around 50 USB plugs from other devices I have used in the past.