Solution:
Devices such as these were unavailable- commercially or otherwise. To design and build from scratch, using off-the-shelf components was the only option.

...And a thought in passing- "...love many and trust few, and always paddle your own canoe."
One of several lessons I learned here is, "You can create anything you can imagine, and you can do it on a shoestring budget- but if you're going to create something for someone else, make sure the shoestring isn't one of your own".