If you go back to the first page, you'll see that it took 2 days for my first 2 Miis to show up, and I was the nexus of this group.
Therefore I got the most Miis the quickest. You'll also see that it took Hoodedsoldier (a really early joiner) 6 days to get up to 18 Miis, including the ones he personally made.
I have the first ~40 from this thread on my Mii, and have for the last 10 months. At the momment, there are about 450 Miis in my parade. It just takes some time.