New Jax can handle Tryndamere pretty well, seeing how you can negate 2 seconds of auto attacks and then stun him. With the rest of your team backing you up, and using exhaust, there shouldn't be too many Tryndamere's you cannot handle.
Also, common items that counter AD champs include any that give tons of armor and or a attack speed debuff. Items like frozen heart, randuin's, and (the already mentioned) thornmail all fill this role.
One last idea is to make sure your team comp has hard CC in it anyway. This helps with any enemy champ that gets out of line, Tryndamere or otherwise (except Olaf).