If I drill down to the t-shirts in the Paizo store section I can get to:
There, if I click on any brand other than Paizo, I go to a page with the t-shirts available from that brand.
But if I click on the Paizo brand link (which points to http://paizo.com/store/apparelGifts/tShirts/paizo) is resolves to the original http://paizo.com/store/apparelGifts/tShirts URL and I'm back where I started.
The link to the Paizo shirt section shows it should have 36 products.
I've tried it with Safari and Firefox and see the same behavior.