I don't know if there is a site just like gamiss but if you want to buy clothes with bitcoin you must exchange it first to $ and paypal as a payment method. Because most of the online shops do only accepts payment with paypal or any other authorized web site. If you are not unable to find some other site like this, well try my suggestion and use virwox for it.
Indeed most of the times you have to exchange your bitcoins to really make a payment on these websites.
I hope there will come more clothing brands that are gonna accept the bitcoin.