During our trip to Holland we spent a day exploring Den Haag, and while there we were able to find all 4 of the Miffy statues there as part of the Miffy Art Parade :)
The first 2 we found are side-by-side in the entrance foyer at the city hall, just to the left of the main doors.
The next Miffy is in Hotel Des Indes and was a little harder to spot. You have to go further into the hotel to the cafe/bar towards the back, and the statue is up on the stairs landing.
The 4th Miffy is in the cafe at Beelden aan Zee Museum, which is in the Scheveningen area to the north of the city. It’s a nice seaside area :)