Heartsteel
Heartsteel is a great choice against Tryndamere. He doesn't do %HP damage, he's squishy and gets popped easily, and the extra range is nice against him.
Iceborn Gauntlet
I imagine Iceborn and Dead Man's Plate are nice against Tryndamere, but I think Heartsteel is usually gonna be a way better choice first item, and you don't really need to build against Tryndamere, as you already typically kinda pummel him.
Swiftness Boots
Swifties are nice as usual, as they're cheap and will help you stick onto him.