I occasionally look at an iCharger with a 'dead' channel for a user. In most cases, the fuse soldered to the circuit board opened due to a bad connection or a bad LiPo causing an issue.
But where to find them? I have sourced them from Mouser Electronics in the past but are available at most large electronic components stores online. Search for 'non-reset-able surface mount fuse'. Typically, they are rated at 15a.
The picture shows a typical fuse. It is about 6mm long and 2.3mm wide.