There are training maps out there that can be used to practice rocket reflect timing. However, training maps spawn soldier bots using the default loadout. The standard rocket launcher is probably the easiest to reflect, but I almost never deflect the Direct Hit and Liberty Launcher successfully because I am not used to the timing and have no way to practice except when I run across soldiers using them in a public server. Is there any way to practice single-player against those weapons with bots?
The only way bots can have non-stock weapons is in Mann vs. Machine. Luckily, it's not terribly hard to edit and customize MVM waves. Check out this thread to learn more about creating and editing waves, and this guy's Facebook page for a download link to a jar file that creates MVM wave files for you.
As for specific wave settings, I would recommend sending an individual soldier once every 10 seconds or so, alternating rocket launcher types. You could also even mix it up with with huntsman snipers and flare gun pyros.