I'm the original poster. I know CB's are dead, but I ride with a couple of groups that use CB's while we ride. We were formerly HOG groups but the HOG chapter disbanded and several of us ended up with non-Harley bikes, like my FJR.
Buy this to connect your Sena headset to CB radio.
They haven't changed them physically since they first released them years ago, so you can find a functioning used one and update the firmware. They can run off 12V, so no need to worry if the battery doesn't hold a charge anymore.
I normally use a GMRS radio when riding with a small group of friends, but have a Cobra HH38WXST that will plug into the SR10 with the same cable that is used with my Baofeng GMRS. I'll use the CB when I'm by myself riding interstate more as entertainment than anything else. Everything can clip to your tank bag, or you can remote mount an antenna if you want to spend the time mounting everything and getting the antenna up higher. This would give you better range.
HH38WXST runs off 12v as well, or a bunch of batteries (8 AA if I remember correctly).
Normally a few HH38WXST units on the used market.
This cable plugs into the Cobra HH38WXST.
It is listed as Kenwood, but pins are same on Cobra. At least for the older models. You will have to do some checking to verify it will plug in if going to the newer HH50.
Lots of choices in online sales for the SR10 and cables. Shop around.
FYI, if you will be running everything off 12V, you will need to put in some ground loop isolation, or you will have a lot of noise.