There are a fair amount of handwired ones, prototypes, higher key count boards or 2 key thumbs as options for farther away thumb clusters as well. You could also try to get more than 3 thumb keys and not use the ones too close to your thumb.
Might be worth looking through if you haven't already:
Honestly could swear I had seen more, but when I checked 3w6, waterfowl, or several others it was just really long thumb clusters. Not actually lower down on the board away from the alphas sadly.
I know this is old but stumbled upon this earlier which appears to be like a gergoplex with a trackpoint as an option:
https://holykeebs.com/products/span
here's the github: https://github.com/idank/spankbd
Not sure if you're up to go get the PCB printed yourself and interested in similar options:
This one has longer vertical thumb keys: https://github.com/erkannt/neuro36
Really far away thumbs: https://github.com/sboysel/giraffe36
One that seemed to have the thumbs farther was draculad, farther than microdox:
https://github.com/MangoIV/dracuLad/
Seen a few places selling kits.
https://www.littlekeyboards.com/products/draculad-pcb-kit
https://customkbd.com/products/draculad-pcb
https://keycapsss.com/keyboard-parts/pcbs/166/draculad-split-keyboard-pcb
https://keebd.com/en-us/products/draculad-keyboard-kit
There are a fair amount of handwired ones, prototypes, higher key count boards or 2 key thumbs as options for farther away thumb clusters as well. You could also try to get more than 3 thumb keys and not use the ones too close to your thumb.
Might be worth looking through if you haven't already:
https://mechdb.net/keyboards?split=true
https://golem.hu/boards/
Honestly could swear I had seen more, but when I checked 3w6, waterfowl, or several others it was just really long thumb clusters. Not actually lower down on the board away from the alphas sadly.