It seems there are no USB sticks with hardware write switch of such small form-factor as Kingston SE9 (39mm of length). There are some alternatives smaller (shorter) than Kanguru SS3.
Kanguru FlashBlu30 - 64mm (8-64GB) / 71mm (128-256GB)
Netac U336 - 67.5mm
Kanguru Defender 3000 - 72.2mm
Kanguru SS3 is long 77mm
searching for a small SD ...