First, yes, you need to have all switches in a stack to have the same firmware software.
Next, do you have a CCO account? Where are you looking for the software? Judging by the fact you have the NPE software pre-loaded on the switch, you're in some country that is not the US. The NPE software is available on the Cisco support site.
Next, do you have a CCO account? Where are you looking for the software? Judging by the fact you have the NPE software pre-loaded on the switch, you're in some country that is not the US. The NPE software is available on the Cisco support site.