You can't, because the API of Blizzard's leaderboards doesn't offer any information about gear. You can only check the leaderboards in-game one-by-one. And even then you only have the highest clear per account, so if the #1 player cleared another GR with another set just one tier lower it won't show up. And from experience the ranks #2 to #1000 just copy #1, so it's only natural that leaderboards always converge to one set. Until someone starts using a different set and discovers that it's strong as well.
Diablorank.com used to have such a filter feature, but it's currently disabled. Going through all in-game leaderboards and taking screenshots is a lot of work and I guess it's not worth it right now to do this where ranks change on a daily basis.