I believe Nintendo randomly gives these out. Usually, though, they try to release them on a real-world or AC holiday. As how to get them, you just have to log into Wi-Fi that day, more or less just open your gates and visit someone else's town or have someone visit you to get it.
By the way, welcome to TBT. If you need any help, contact me. Always great to see a new member talk about AC.
yea certain days on WIFI u need to be on wifi with a friend and then when u close ur gate or leave go to ur house a letter from nintendo will be there with a special item.
January 12 - Coin
January 26 - Red Tulip
February 13 - 1,000 bells
February 14 - Lovely Loveseat
February 21 - Top Hat
May 5 - Sombrero
May 8 - Daffodil