Frankfurt Zoo is the main breeder of freshwater crocodile Crocodylus johnstoni. They have held a breeding group since early 1990 and have achieved the first overseas hatchings since 1994. They have bred the species regularly since and have sent young individuals to various collections in Germany, Czech Republic, Switzerland, US and even Thailand.
The second European zoo to breed the species is Basel Zoo (first breeding attempt 2018, first 2 hatchlings in 2020 - the breeding pair (26) are offspring from Frankfurt).
I am unsure how many individuals the Frankfurt Zoo started out with (someone mentioned 1.4 at some point, at least 2 females are regularly laying and the zoo has been hatching out eggs).