Hi Daniel,
I've tried without success to find these tables even with the tracing tool (ST05). I think these data (mapping between DSO and datasource fields that are not in RSOSFIELDMAP) are not stored in tables.
One workaround is finding this relation in the transformation program:
Enter in the transformation --> Extras --> Display Generated Program --> Look for the lines after the pattern *<<< Rule ID: '1'.
If you want to search in all your transformations programs, you can use the tcode CODE_SCANNER with the pattern " = <_YS_SC_1>-". In my system I noticed that the transformation programs usually starts with GP4*:
Result:
With some excel manipulation you can split the infoobject and the datasource field.
I hope this helps.
BR,
Marco Modesto.