I haven't gotten any new 'limited' Kao coins in what feels like 3 months. I think right before a huge new set was added was the last time I got one.
Weekend use has been steady, and although it is statistically possible to not get any from the remaining 1/4, it feels more like there is a bug or mis-weighting going on somewhere.
Duplicate coins also don't have a distinct indicator for these (at least that I've noticed) so no way to tell easily if I'm at least still getting dupes.
I'll probably just remove that - we used to introduce new coins each month (which were limited, as they were only available for the month), but it doesn't make as much sense now to have it (that was a few years ago).