Identify PCB component from LED circuit
It looks like a bridge rectifier but I can't think why there would be one in a 12 V DC circuit.



simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. A bridge rectifier consists of four diodes.
There's no scale reference in your photo but I'd guess that's a 1 A device and so is unlikely to be in the actual indicator lamp circuit as these are normally 21 W lamps drawing nearly 2 A each when hot and a lot more when the filament is cold. It's more likely to be rectifying the power for the flasher unit itself.
They're available from any electronics component supplier. You'll find a parameterised search on any of the large suppliers. Select something that's rated for 50 V and whatever current you think is required.