Just send Tim an email through his website! I have no idea if he will cut a deal but he might.
First, I use this mount. This lets me mount Bowen's Mount accessories as well as holds the speedlight much better than the hotshoe mounts. It also puts the light closer to the center which fills the modifier and gives you better results.
The Octabox I am using is this. It comes in two sizes, 37" and 47" http://www.amazon.com/CowboyStudio-Octagon-Umbrella-Softbox-Monolight/dp/B00E8NMN96/ref=sr_1_1?ie=UTF8&qid=1445896631&sr=8-1
I like this Octa because it folds up like an umbrella, and is super quick to set up. Its very stiff at first so I recommend setting it up and letting it stretch out a few days before trying to use it on location. The Octabox uses the Bowen's mount, which works perfectly with the Bowens to Speedlight flash bracket.