When you say driver, are you looking for an Indi driver for a flat panel that is not "FlipFlat" (indi_flipflat)? Or are you looking for a flat panel device itself that is not one of the Optec (Alnitak) offerings?
If a flat panel device itself, have you considered any of the inexpensive DIY flat panels described on a variety of internet sites. They range from rewired (to add a controller) electroluminescent panels to LED based devices controlled by a microcontroller like an Arduino. Many of these use the drive protocol initially defined by the Alnitak Generic Serial Commands (Optecinc.com site has this document) coded into the Arduino and connected to the "system" via USB.
I have one such LED/Arduino based system I am currently working the bugs out of. Kstars/Ekos/Indi controls it using the FlipFlat driver.