A decade ago I bought on eBay a big box of Casio service manuals (mainly 4-bit/squarewave era and Super Drums stuff) but have no intact scanner.
Around 2000 also W.D. Greenhill used to sell Casio service manual copies (likely only as PDF) but at that time I refused to throw money into the throats of that doubtful business. Now their Casio stuff is likely all gone (nothing mentioned on their website). I remember they had e.g. those of Symphonytron 8000, Casiotone 201, 202 and VL-5 those I never saw anywhere offered again.https://www.wdgreenhill.co.uk/contact