It would have to be able to run three of them at the same time, in an extended desktop fashion. This may not be possible.
You could use a FPGA?
The one SPI in from the Pi, to 3 SPI outputs to the LCDs.
Considering the price of FPGA dev tools you might be better off using Pi Zero's and seeing is this works
Probably would need to use USB ethernet gadget mode, but that's a bit over the top for your ap.
Maybe there is a micro that has 4 SPI ports, one slave, 3 masters and enough ram to hold the image data.
For weird stuff like this I also go to the Cypress PSoC family, 32bit ARM core with programmable CPLD type blocks
A 4200L micro can fit 4 SPI's no problem, but only 32K SRAM, if you need more you will need to use another chip.
You can get ARM Cortex M0 micros with 256K SRAM.
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