Come on, I can't believe you've actually looked. The search "spawn random"
comes up with dozens of threads - many of them solved - on the matter, with multiple approaches.
In general, with the free version of C2, the approach is: generate a random variable (rounded to nearest whole number) within your desired range; then create a bunch of events to spawn objects, each triggered by a different value of that variable.
With the paid version, you get access to families, which can do this all for you in a single event.