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Cosworx
Carries a huge selection of boots. Also carries petticoats, wigs, shoes, makeup, wonderflex, fosshape, etc, for people, and then also wigs and outfits, etc, for dolls.
Funky Boots
Hot Topic
Hot Topic mostly carries rave and goth clothing, however in addition to that they have a massive selection of boots of all kinds... including combat boots, gogo boots and the like. Also check out that they have a larger sizes.
The Shoe Palace
Also has a wide selection of shoes (lots for anime based costumes!) and they have shoe sizes 5-15!!