Are you playing the DOS version or the Windows version?
If it’s Windows I can send you a save for the beginning of Ch.4 but not right away. I am playing through again in bits and pieces but I think I’m only up to Ch.3.
ps If you want to mail me a blank CD-R and return postage I can try to help with replacing your damaged disk 3, too. Email me firstname.lastname@example.org if you like.