Many Loadstar programs were written in BASIC, and didn't need source. I should say that I had several programs published in its issues, and some of them had machine code components. I don't remember having to submit source code--indeed I couldn't, as many of my routines were written by bashing together opcodes looked up in the C64 Programmer's Reference Guide. No assembler, no monitor, just data statements and numbers. Nearly all of my programs were before Issue 100 though, I wouldn't know if their later issues were made with a different policy.
Beyond that, a number of programs were first published elsewhere, and it seems unlikely that Polarware would have handed over their source code.