The number of 3DS Play Coins you have

300, and that's the maximum of what you can get.
I only used a lot of them in StreetPass Mii Park, in order to solve the rest of the puzzles, and in order to complete the quest, but it's now fixed again.
 
I will get 300 by shaking and watch TV and change time, I got 30 pokemon in 1 day
 
Eew!
I don't want to even think what you're doing with your 3DS! (O.O")
 
You can use Dogs if you change your favorite animal in your spotpass mii settings
 
>>Falco
It's StreetPass, not SpotPass.
StreetPass is the green thing, local wireless.
SpotPass is the blue thing, online wireless.
 
>>Falco
Just go with your 3DS in your pocket, to your work, school, or whatever, and get back home.
Repeat this every day for 10 coins a day.
After a while, you'll have 300 coins without cheating.