Here one I've not seen before. they're $69.50 on eBay, it's rather interesting, probably more for a antique radio enthusiast than a neighborhood broadcaster but it's still cool. No specifics about part 15 are described but it's seemingly stands to reason it's part 15 compliant. Here's a few pictures, there's more and a video demonstration too. Copy of description is below..
AM Transmitter Bluetooth, USB, FM SD Player Stream to Your Vintage Tube Radio https://www.ebay.com/itm/127897973525?
Combination AM transmitter with built in player that accepts bluetooth, USB, and Micro SD Media as well as an FM tuner.
This is great for those that live in rural areas without AM reception or for transmitting period correct music/programs to your antique vintage radio.
Transmit your favorite music, radio shows, playlists, or other audio to your old antique tube radio through this AM radio transmitter!
No modifications or alterations need to be done to your vintage radio.
Includes the following operating modes:
Bluetooth - Pair your audio device with the built in Bluetooth receiver on the AM Transmitter
FM radio - Select the FM feature on the player and extend the White FM antenna wire
MicroSD - Put your favorite music/audio on your Micro SD card (up to 32GB) and insert card in the memory slot.
USB - Put your favorite music/audio on your USB stick and insert in USB port on front.
Place transmitter near your radio, extend the yellow antenna wire and transmit to your radio on 1000 kHz on the dial.
The transmitter is powered with your standard USB-C phone charger & cable (not included).
Note: Many USB-C phone chargers are noisy and create interference. a separate black ground wire with alligator clip is provided to connect to a ground terminal or radio chassis to eliminate interference.
Easy to use with included instructions.
1. Dual decoding supports music in MP3/WMA/WAV
2. Function: Bluetooth 5.0+lossless decoding+call+radio FM+AUX+USB+TF card
3. Support external audio source input LINE IN
4. Support radio FM, search frequency band (87.5MHZ-108.0MHZ)
5. Bluetooth transmission distance: within 20 meters
6. Buttons: three-button control, VOL-/AUTO/VOL+