Sorry to hijack Ron's thread, but if you need some information about snowy assets Adam, then read on......
I think it's too obvious to say the DLS and search under the 2 keywords - snow and winter....:hehe:
You have the trees done by Jankvis, Dave Drake, Railcentre and Tafweb. You also have houses, factories, industrial units, stone walls and fences by Railcentre and tafweb all snow covered. If you search on CAB, Roger Cabo did some alps stuff, particularly, some spline telegraph poles snow covered.
Bob Sanders is currently creating some terraced housing also. However, these are more UK-style buildings and I'm unsure if these are of any use in a North American layout as such.
On the 3rd party website approach, there are a lot of links I have put on here from around Europe, for houses, stations, signal boxes, etc, etc. I also found some winter trees with no leaves on done by our lovely Trainzy friend Alberte and some other bits and pieces from Spain, though as they don't see much snow in real-life there isn't much call for snowy objects on Spanish routes.....
I don't remember seeing any other snow-covered railtracks apart from those you know of done by Vendel, he also created some snowy farm fields and other textures on the Painted Grace section at HO Trainz Hungary, worth checking out. There are lots of different tracks from the Czech and Polish creators, some are on a white ballasty type substance, so you could say it's snow, nobody will notice the difference.
Best to try our Eastern European trainzers, who have more snow than we do....I also found some apartment blocks and flats from a Russian site, but even though they aren't snow covered, they are white in appearance and may look good if you had them far away in the distance from the tracks on a layout. I found some superb splines depicting muddy, wet roads and tracks with puddles on, which are very suitable for farms, etc from Roltrainz in Hungary, he also did some great little bungalow type houses with snow on the doorstep, very nice models.....I also found some farm tractors from France which look quite good and Rox did a winter collection on the TrainzItalia site.
Have a search to see if anything takes your fancy, and don't forget that a lot of websites have links to other websites that I haven't searched on fully, so you might be lucky and find something I aint seen yet.....:hehe:
Good Luck.
Cheerz. ex-railwayman.
http://haegar-trainz.de.vu/
www.ibertrainz.eu
www.ibertrainz.com
http://www.spaintrainzrutas.com/objetos.html
http://www.virtualbreizh.fr.nf/
http://j.moureau.free.fr/
www.roltrainz.hu
http://www.trainz.hu/
http://www.bogesz.cjb.hu/
www.trainzitalia.it
http://trainz.dino.sk/sk/index.html
http://tsmteam.ru/Default.aspx
http://www.trainz.ru/
http://piter-trs.3dn.ru/load/
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http://trainz-trs.ucoz.ru/
http://www.trainsim.ru/
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http://dikobraz64.xf.cz/
http://trainzpedro.cz/
http://www.trainzmotion.cz/
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http://www.trainz.org/ptt/index.html