Yes, the modern(ish) film holders for 9x12cm and 4x5" are the same outer size. (These outer sizes are internationalized, at least since about the early fifties or so. This means that 9x12cm and 4x5", 13x18cm and 5x7", 18x24cm and 8x10" respectively all have the same DDS holder outer measurement. It's just the film size that differs slightly.)
The cm sizes is/was the common european norm, while the inch cut film was the norm in the US (and more common in the UK). Nowadays, it's even quite hard to find cm cut film in Europe as the inch cut films are more common.
So, if you are looking at any camera with an "international" back, i.e. any view camera from the fifties or later, it should take standard size film holders.
About 9x12 film in the US, Freestyle sells one film (Efke PL100), but there should be other retailers available. If you look at e.g. Fotoimpex.de you can see what is available in Europe. They will also ship to the US for a cost of €20. (If you really need film in 9x12 size that is.)
//Björn