Not the best solution, but if you just want the appearance and are not too concerned about "features", the scanner that came with the Diamond Select Medical Tricorder will do in a pinch. It has a sound chip but it is very faint, at least mine does. Also, the spinning action is achieved with a "flywheel" gear rather than an electric motor. It's almost impossible to steadily "flick" that wheel to achieve continuous motion without it looking very obvious. I'm no engineer, but if installing a motor was an issue, for Diamond Select, I wonder if a clockwork element could have been inserted, something akin to a "pull back and go" mechanism? In theory, one would wind it and pressing the button would engage a rapid rotation for several seconds, enough time to "wave" the prop for a "sweep" or two. The button would also play audio for the duration.
Funny enough, the scanner that came with the PlayMates Toys version, had a chip and speaker that would almost deafen somebody! Alas, the "spinning" effect was achieved by swirling one's wrist, like stirring a pot. The developers must have referenced the vintage Franz Joseph plans because instead the transparent section was a convex disc, almost hemispherical. It was also a bit oversized (probably to house the electronics of the 90s) while the tricorder itself was closer to 3/4th scale.
If you can't get a Diamond Select scanner, but
do have access to a 3D printer, here is a collection of .STL files to assemble an entire TOS tricorder, including a scanner!
Larger kit project to build a tricorder from the classic series. | Download free 3D printable STL models
www.printables.com
You don't have to download all the files, apparently you can select specific ones required for just the scanner.