Prime has dropped of of all units with CPUs slower than 900MHz.
The Roku Wikipedia article at https://en.wikipedia.org/wiki/Roku is a good reference to work out systems with > 900MHz and composite output.
The 5th generation Roku Express+ (3710 and 3910) fit the bill (the "plus" is the key to composite output) and that's the end of analog output.
You might instead invest in an HDMI to composite adapter and just grab any HDMI Roku. They sell on Amazon with the search term "HDMI2AV" or "HDMI to RCA." You want the "Digital to Analog" version, NOT the "Analog to Digital" version. Be careful to get one that takes HDMI as *input*. They are about $10-$20 USD. And they will need USB external power, so a Roku with a USB port will provide that little power or you need to get a little USB power adapter.
At that point, any HDMI device can talk to your TV.
"HDMI to RCA Roku" is probably the best search for the device you need.