As he showed above, get T10 wedge bulbs.
I got some cheap LEDs off ebay as well. Keep in mind that electricity only flows through LEDs in one direction, unlike a normal bulb, so if you plug it in the wrong way it won't turn on. It's not broken though. Just swap them around until they light up. You may want to keep a normal bulb for the turn signal indicator though because it won't work as intended otherwise.
You can literally reach behind the gauge from under the bike and pluck out each bulb to swap, although its a tight fit. I did it blind, but you can just count how many you've swapped. The bulbs pop out super easily. There are 7 bulbs total.
Picture of the back here:
https://www.ninjette.org/forums/show...58&postcount=5