The Misadventures of Tron Bonne
When you've given a servbot the red heard parts (get from #9 in the gym after a few missions) speak to #17 in Tron's room. He will ask you to take a rest and your favourite servbot will go to the casino, where you can play high and low, and bingo.
On mission 1 of the city, as you're bound to find items, take the servbots whose brains you want boosted, along with you.
Go to the ancient ruins and get the fireworks and pipe. Now go back to the gessleshaft and go to the lab. Give the fireworks to the servebot in charge of gatling development and give the pipe to the servebot in charge of bazooka development. Now all you need is a lot of zenny to buy the gatling gun and bazooka. NOTE: before you give the servebots the fireworks and pipe you have to buy the gatling parts and bazooka parts.
Thanks to Revolution readers Glyde and Nick Bunzli.