Use the Uniden BC23A. Works great in my truck with both HP1 and 996p2. Has a right angle plug and is a stereo plug which is what you need on the Homepatrol units.
The best bet is just get a "cheap" bluetooth speaker with an input jack. I use a "keyringer" and it works great, and will run several hours without being recharged.
I use this Anker Ultra Portable Pocket Size Wireless Bluetooth Speaker with 12 Hour Playtime, NFC Compatibility, Ultra Compact Ring Box Size (Black) - A7910 $19.99 and it works great on my HP-2.