I found this board on AliExpress (https://www.aliexpress.com/item/1005003540616473.html?spm=a2...) based on the CM4 and with 3 cellular modems. That could also be a good candidate.
Also found this one (https://www.gateworks.com/products/industrial-single-board-c...) US-made and has 3 minipcie slots (other options available with 2 and 4)