If you need one for your own costume, you can get it here.
For reference, this is the costume I'm going for. It changes from episode to episode, season to season, so I really just had to pick one that I was happy with.
It looks like he's wearing some pretty straight forward dark grey slacks, which will be next on my list.
This is my primary reference picture. Navy shirt, grey suspenders, white buttons, white undershirt. No problem