The release notes for CUDA 10 suggest that 32-bit support may have come to an end (after it had been gradually phased out in previous releases):
https://docs.nvidia.com/cuda/cuda-toolkit-release-notes/index.html
Various internet news bits indicate that 32-bit support was removed from NVIDIA drivers during 2018, with the exact time frame slightly differing by operating system. Official announcement: https://nvidia.custhelp.com/app/answers/detail/a_id/4604/
So with 32-bit support removed for tools, applications, and drivers, it is not surprising you cannot find 32-bit components in the CUDA 10 installer. This doesn’t look like an oversight, more like part of the plan.