There was a thread about Focal a while back:
viewtopic.php?t=481
It's not entirely clear to me from that thread whether anyone has any actual source code or whether it's all just disassembler output.
What do wish to accomplish? Are you just trying to port it to whatever 6502 system/simulator you're using or do you want to modify it and/or extend it? I tried porting the "disassembler output" KIM version. I just supplied an input routine, an output routine and a BRK vector and, though I did not test it extensively, it seemed to be working and the simple things I tried did pretty much what I expected. (Though I used the disassembler output as a guide, I ported the object code, rather than the assembly. I did not attempt any relocation, which made the process far easier than it otherwise would have been.)
Even without meaningful labels or comments, the disassembler output looks like it would need a little more work before being used. For example, there are several tables of (internal) addresses that were disassembled as constants rather than labels, so all those addresses would be incorrect if only the origin were changed.