Take a known good spoke and look it over carefully and then match.
-check the headstamp on known correct spokes: is there a mark (say, a "U" or an "R" or a brand stamp)?
-What is the shape of the spoke head - domed or flat? Some companies polished them down, some left domed.
-what length is the spoke? Lots of Torringtons in middleweight and ballooner sizes, but not as many in lightweight sizes.
-What color is the finish? Light grey? Darker grey with a rough/thick finish? Anti-rust coatings varied.
-Make sure you match the shape of your known good spokes (double-butted, straight gauge, tapered, etc)
-How long is the elbow on it? Brands varied on the length of the spoke elbow, and newer spokes often have longer elbows than older ones.
My philosophy is to match as many of those elements as possible without worrying too much about the brand. Usually I'm looking for a handful of spokes to round out a wheelset where a couple need replacing. If the spoke essentially matches what I have already, I don't care too much about brand. I'm sure museum-grade collectors are pickier than me though.
The odds of finding verified, known Torrington lightweight spokes possible, but you'll need to be patient. You'll want to buy from a bike collector who knows his stuff, and who probably has spokes he knows are Torrington (maybe still in the correct box). Buying "in the wild" on eBay from guys with bundles of unknown spokes usually will yield something made by Union in the 1960s-70s, at least in the 26 inch lightweight bike wheel sizes.