daniel333,
When I create demonstrational apps, I often find that I cannot find a data generator for my requirements. I don't actually have much experience with Apache of IIS logs, but if this was me, I would take a bunch of common log events (probably find lists of these online), and then decide which sections of the logs need to change with each log event (e.g. date/time, ip addresses, etc.). I would then write a simple bash script that uses "while true; do" loops and place random (depending on the content you could use something like bash's random function, or I like to simply use the "shuf" variable) content into STDOUT/log file and feed this into Splunk. This could then be built on if you need more organised logs.
There are probably much tidier methods for achieving this in a python script of something, but it's whatever works for you.
Also, with regards to your "lost" question, you can find past-posts/questions in your profile section (click your name at the top of the page).
Regards,
MHibbin