If I need a new receiver and can't find one that is exactly the same as the one that came with the radio, can I get one with the same amount of channels and from the same company and use it with the radio?
There are various digital protocols, and many receivers are able to handle more than one protocol (and so can a few transmitters).
It looks like that transmitter uses "AFHDS 2A", so you need a receiver that can handle that.
That receiver (FS-R6B) says "AFHDS" on the label, and there's a big complicated chart (the 5th image) showing which receivers handle AFHDS 2A, but I can't see the FS-R6B on the chart so it's not much help. The binding instructions imply that it might do both.