Google is your best friend. I just googled with the words elevated model layout. I got this page here:
Modeling the New York City Subway
There is more out there. Just google it up.
Here, I found this:
Walthers Model Railroad Mall -- product information page for 920-31016
There are a lot of subway modelers out there. A lot of them model in O scale 2 and 3 rail. Here is an O scale forum for it. they may be able to steer you to some HO info.
Subways/Transit/Traction - Forum Powered by eve community
Keep yer countin' to your own damn rivets!