If you are an engineer, get two of these and that's +40 shadow resist alone.
http://db.vanillagaming.org/?item=18658The Brightcloth set is really cheap and has a lot of shadow resist as well:
Cloak +7, Gloves +11, Legs +16 & Robe +15
http://db.vanillagaming.org/?search=brightclothI'm not sure if these patterns are in the game yet. The twilight texts for the Silithus quests aren't dropping and they were usually in your goody bag you'd receive after turning in sets of 10. It shows a super low drop rate (0.02%) but I don't think I've seen the recipes for sale.
http://db.vanillagaming.org/?search=runed+stygianFor a necklace:
http://db.vanillagaming.org/?item=13473For rings:
I think there are green "of shadow resist" rings (and maybe necklaces and possibly cloth armor) but you can't search for them in the databases off of the random enchantment.
There are also potions and flasks that up your resists too.
Hope that helps some.