I picked up a pair of Ultimarc’s Ultrastik 360’s. They’re quite nice but I really didn’t like the existing ball top, or the selection of options that Ultimarc had to offer. Fortunately I noticed in one post on BYOAC by Paradise Arcade that their Seimtsu 6mm ball tops do in fact fit on the U360. I picked up a pair of ball tops from Paradise Arcade (purchased 2 pair, but only one pair showed up, hopefully that gets fixed), a green bubble top and a violet bubble top. For all you out there wondering, they fit perfectly and look wonderful.
Update: Just gave Paradise Arcade Shop a call and the mistake was corrected and my two missing ball tops were sent out immediately. Great customer service. Thanks Susan!