I think you missed it. They have a sample button in red along the top of the page. They didn't specify what paper you'd get, but you could email them to see if metallic could be sampled. They do have add-ons to the sample packs.
I missed that, but I don't see there where they have samplers of just metallic paper. Maybe I'll shoot them an email. Or, they have a 20 pack of the Polar Pearl Metallic in 8 x 10 for just over $20. I might just try a pack of that. It seems to have very good reviews.