I've found out a road arch exclusively available in the Japanese version of The Sims 2 in "objects.package" under TSData\Res\Locale\Japanese\Sims3D.

I found that it contained some files for the archway and I guess they're there to override those for the road arch from the English Sims 2. Are there ways that I can simply clone the object and put into my game?

Ooh~ I've figured that out myself. I can clone it with the object workshop just like cloning other objects. Sorry for the stupid question. :P