Where can I download Sketchup 8 and Sketchup 2013 Make?

IF you have downloaded the Make 2013 installer, after 30 days Pro trial, the program reverts to the Make version of SU, with permanent free licence for non-commercial use.

IIRC the v8 free licence does allow commercial use, but you will need to read the licence to be sure. That free version wasn’t then called Make.