itch.io

There's a few mods available here:

mega.co.nz/#!3QcnAbwD!UlAsIhVPdh-Cr3Aeflpiv-M06YdTSPU6yOq4fOSCtUE
mega.co.nz/#!FZVCwA4b!GCSv2FW1yFv4KeCXe6S3hnr0A_hJUt_VbUvlkyyTkQI

from:

https://www.gog.com/forum/octodad_dadliest_catch/a_howto_on_custom_levels_in_the_gog_version_of_octodad