While the Brotherhood of Randis is the group that obtained the Cache, the Cache site was on Antallos, out on the OA/DC periphery region. Specifically Antallos III, aka Port Krin. in 3051 they fought Fuchida's Fusiliers (a merc unit that had just recently left Fedcom service to go pirate) for the site, described as an SLDF cache. the site apparently had, in addition to several Rampages and other RWR mechs, a large number of Age of War designs.
at least, according to the Sarna entires referrign to the event. sources listed for them are the Periphery sourcebooks, both the old one and the newer 2nd edition one, as well as Jihad Conspiracies: Interstellar Players 2. not sure what details are from what, though i'd guess the details of the cache came from ISP2 since rampages and "age of war" didn't exist as concepts yet when the two periphery books mentioned came out.