If you don't mind eating the shipping.... https://www.akishop.jp/joystick-parts/344-lb-35-keikou.html##
I ordered a handful. A handful of neon balls.
Focus attack has pre-order for neon buttons (15% discount too). Sadly I don't really like seimitsu screw-ins, plus they don't come in 24mm (yet?), still hard to resist.