Please add the conda-forge channel to your list of channels with the use of following command:
conda config --append channels conda-forge.
It will inform conda to also look on the conda-forge channel when you try to search for packages. After that you can just install the two packages with following command:
conda install slycot control.
The channels are the servers for people to host the packages on and the community-driven conda-forge is usually the good place to start with when packages are not available via the standard channels. I have already checked that both slycot and control are available there.