Silk Swatch & Spider Silk Farming Locations
All you need in order to create a Silk Swatch is two Spider Silk. You'll need to combine this Spider Silk in a Sewing Kit that you purchase from a vendor or in a Loom which you can usually find in your race's home town or in a major city like Plane of Knowledge.
Spider Silks are farmed off all sorts of different Spider enemies throughout the game. Below is a list of all the good farming locations that I know of for Spider Silk; the best farming locations I know of are listed first and further down the page you'll find Spider Silk farming opportunities from later expansions.
East Karana - Spider Silk Farming Location
This is without a doubt the best location in the entire game for you to farm Spider Silk. It's even better than the location in Goru'kar Mesa (The Serpent's Spine expansion) if you're only after Spider Silk and nothing else.
Misty Thicket - Spider Silk Farming Location
This location is good for Spider Silk if you're too low of a level to hunt in East Karana or for some reason can't get there.
North Ro - Spider Silk Farming Location
This location is good for lower level evil races that can't handle East Karana yet and hunting in Misty Thicket would be too risky. There's a decent amount of spiders in this area and it's extremely close to the Commonlands tunnel which is a pretty big bonus for a variety of reasons.
Goru'kar Mesa - Spider Silk & Spiderling Silk Farming Location
This location is one of the best locations in the game for you to farm both Spider and Spiderling Silk. The Spiders you find in Goru'kar Mesa once defeated will spawn multiple mini Spiderlings which you can defeat and claim their Spiderling Silk. It's a nice added bonus.