Do bluetooth speakers for cars exist?

If your current head unit has an aux input, you can get a Bluetooth receiver.

You can buy a gadget for $20 or so that plugs into cigarette lighter, receives Bluetooth and broadcasts FM on selectable frequency so you can use your car FM radio. Works well and sounds as good or better than broadcast FM.

I have the gadget mapman references and it works great, here is a link to Amazon where I got mine.

https://www.amazon.com/gp/product/B01DZKERVY/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

Yes that is what I have also.  Works great.   Be aware if left plugged in and on when not in use it may cause some interference with some FM broadcasts.  Best to simply unplug when not in use.