The nice thing is, if you're going for some Chicago flavor but not exact and perfect duplication of a particular line/era, there's always something out there on account of just about every big time railroad in the country being in Chicago. I've seen HO and N bilevels in RI bright red, I've seen HO bilevels in CNW, brw/org RTA, and Amtrak. I seem to remember an athearn LIght blue RTA F40PH, and I would imagine somewhere on ebay there's a Metra blue F40PH. Now pick a couple of geeps or SD40's from your favorite class one and some doublestack cars, and you pretty much have a credible Chicago layout.
Now comes the tricky part - my ideal Chicago layout has South Shore electrics and the bottle train between riverdale and burns harbor. CSS MU's are generally >$150 on eBay, I've never seen a bottle train or GP15-1's in any scale, and don't even get me started on catenary for model trains... couple that with an apartment, no job, and the law school workload and it looks like YouTube is my trainset for quite some time to come.
The new Acela: It's not Aveliable.