I would like to do summer school this year but cannot find a list of what courses are offered
in the spring and summer semesters - where can I find this info?

The classes won't get listed til about February or March. Until then they don't know if they have the staff.

A lot of courses, though, are offered every single spring and summer. All first year econs and 2g03/2GG3/2H03/2HH3, for example, as well as all first and second year core math (except STATS 1D03 which is only ever offered in one session in winter).

A lot of other first year intros, like physics and chem, are always offered every summer.

Spring classes aren't until May 6, and Summer classes June 24... so there is a lot of time. They won't be posted until closer to then, as mentioned here.

Once ready you can go to Mosaic, and navigate to Student Centre > Academics > Search to search for classes.