Hi,
Niel provided you with a link to the Spanish System 7.5.3.
If I may expand a bit on this.
The download consists of nineteen floppy-sized MacBinary (.bin) files. The idea is to transfer the files to the hard disk of the LC III. It is usually better (necessary, if a PC is used for the download) to keep the MacBinary encoding intact until on the target machine (where you will need an appropriate older version of StuffIt Expander for the decoding). Once decoded, place the nineteen files (one .smi and eighteen .part) in a common folder. The segments together constitute one large disk image. Double-click on the first (.smi) file; this will mount the entire image. Launch the installer in the thus mounted image. For a Clean Installation procedure, see Step 7 and Step 8 in
KB article TA44452 (disregard the information about System 7.5.5 for now).
Jan