the service manual says that they are the "wedge" type bulbs. i did a search on ebay using "wedge LED green". there basically seems to be 3 different types of wedge bulbs. i couldn't find an exact bulb type number in the manual...so i wasn't sure which one it is. based on the pics, my guess is that it is the 194/168/158.
the problem is not to get too large a cluster otherwise it won't fit in the opening. although, if you don't get enough LED's, then the light will be dimmer than it was stock. also, i am pretty sure that those are polarity specific, so if one way doesn't work, you gotta flip it 180 degrees and try again.
also, looking in the manual, it didn't specify exactly how many bulbs there are. i was thinking that maybe it is one per gauge, but since the speedo is so much larger, maybe it had two? looking at the pic of the back of the cluster was not very helpful either.
then, i was also thinking that since there is a slight blue tint to the gauge, that if you put a green bulb, it MIGHT be a slightly different green.... slightly bluish green. and if you got a yellow bulb, it probably isn't blue enough to give you a true green either. was thinking that you were still better off going with the green bulb.
anyways, after re-reading my original post, and realizing that i was guessing on most of the info, i thought it best to delete my post and let someone who knew for sure to reply instead.
edit: ooh, found this on another forum. not sure if the guy is on here as well. maybe you can pm him.
http://www.kawiforums.com/showthread.php?t=128927