Squirtle will be the fourth Pokemon in the Funko Pop line so far. The first was Pikachu, who showed up as a Target Exclusive in July 2018. Bulbasaur, the character who is number one in the Pokedex (and maybe also in some people’s hearts) showed up in February 2019. Charmander was announced in March 2019. This means all of the original Kanto starters from Pokemon Red, Blue, Green, and Yellow.
In addition to the Funko Pop Pokemon figures, the company has been releasing A Day with Pikachu line of figures. These were announced in February 2019 and the first figure, One Lucky Day Pikachu, made its debut in March 2019. Each month, a new one appears, with the last one showing up in January 2019.
The Squirtle Funko Pop will be released in the near future. Bulbasaur and Charmander are immediately available via a number of different retailers.