https://www.cl.cam.ac.uk/~mr10/Archive.html
From the README file:
This archive contains some sample files relating to BCPL and the
Tripos portable operating system. They were mainly written between
1978 and 1982.
There appear to be files for the BBC Micro implementation in there, too:
This directory (Archive/bbc) holds files relating to the BBC BCPL
System.
The directory Archive/bbc/bbccin holds object modules of the BBC BCPL
system and the 16k BBC BCPL sideways rom.