ARoss wrote:(Also frustrating to find opto switches in bulk).
I got mine (by the hundred) from here:
https://www.rapidonline.com/kingbright-km-4457f3c-side-infrared-emitting-diode-72-8966
https://www.rapidonline.com/kingbright-l-610mp4bt-bd-phototransistor-72-8968
It looks as though the phototransistors are about to be discontinued though. Interestingly each pair costs about the same (30p) as they did when I posted my design (nearly six years ago) here:
http://forum.hauptwerk.com/viewtopic.php?f=21&t=10628&p=89281#p89281
I, and others here, have experimented with slotted photo-interrupter modules rather than discrete components, and even with reflective photo-detector modules. Both of these can usually be sourced on ebay quite cheaply. If going down this line I'd recommend getting a few first to see if they work for you before buying them by the hundred.
Nick