Much software has likely been lost forever, basically everything that was not released in printed form. Fortunately, listings were popular back then.
Kitbug was a rudimentary monitor that fits in 512 bytes, distributed with the National Semiconductor SC/MP kit and published in the "SC/MP Kit Users Manual" in appendix B. It communicates serially using a software UART, so changing the baud rate requires to change timing constants in the code.
The archive contains the original assembler code from 1975. The binary can be built
with a small preprocessing script and
Elektor distributed software on audio records to be read with the FSK modem originally made for audio tapes.
ESS-002 contains small programs that play songs: Silent night,
Oh Tannenbaum, Hark, Jingle Bells and Mary had a little lamb.
The assembler source was reconstructed from a disassembly listing published
by Elektor 1978, again ready to be assembled with
ESS-004 contains NIBL-E and two NIBL programs. There is no source code for NIBL-E. The changes probably need to be obtained from disassembling the binary.
Most cards of the NDR Klein Computer were accompanied with diagnostic software to verify their operation after assembling them and I followed that tradition for the CPUSCMP board.
There is a simple boot ROM for the BANKBOOT card that moves code to address 0 in RAM and starts it. Included are images for KITBUG and NIBL, using 600 baud (2 MHz) or 1200 baud (4 MHz).