I found the Grand Staircase model..
I am wondering though if there is a more modern version available, ..

A very nice, modern one was posted recently in SourceForge 3D models 354 (albeit in rar format, but there are online tools to convert to zip). If you are looking for something specific, you need to look around the web. The obvious starting point being a 3D warehouse stair search (.dae and .kmz files can be imported directly).

I agree that more staircases should be available specifically for SH3D, at least the basic available shapes in a couple of flavours) I am putting together at collection of the staircases I have used. However, the models need some more work. One example is a replica of a standard (relatively) modern staircase in SF 3D models 329. ok