I recently bought an amplified speaker mic designed for the little Elecraft HF QRP rigs, but it works great as a receive only speaker. Its not particularly cheap but I find it worth the price for my Elecraft rigs. Check out the AlexMic:
https://www.hamradio.com/detail.cfm?pid=H0-015773
I also bought a case of odd amplified speakers made for use with gas masks. They used a throat mic to pick up the users voice and the amplified speaker clipped to the front of the user. They are about 3" across with a 2 position volume switch and have a big clip on the back for mounting to stuff. They run for a long time on 2 AA batts.
I poked around inside one and found the mic preamp has some radical equalization for the throat mic but feeding in audio from a scanner upstream of the mic pre makes some nice loud audio. With a little bit of work these would make one of the best remote amplified speakers I can think of for portable scanners.
I might put several of them on the RR swap pages, otherwise they are made by Audiopack and the P/N on the speaker is 19398, but I don't see any info online.