I'm not sure if this helps, but I've found that dcl_saints_dlc_df.tga is referenced in sp_vtol01_saints.cvtf_pc and sp__vtol01_saints_0.ccar_pc, within the str2.
I opened them with a text editor, then searched for all references to .tga
Yes, my friend, I found the same things where it's referenced in the .ctvf_pc and the .ccar_pc, but no clue as to where that actual texture file is located.
Thanks for your help.