I can vouch for at least one of these online shops -- Qiyi Motorcycle Accessories -- as I know the owners and have purchased items in their retail shop in Wenshui Lu here in Shanghai. Simon Wang (aka 王俺云) and his wife are avid motorcyclists and put their heart into this business. They don't speak a ton of English, though I've been encouraging Simon to put in the effort.

513 Wenshui Lu, a couple of km east of the North-South Elevated up in northern Hongkou district (虹口区汶水路513号), a bit east of Cello's BMW shop.
Simon's mobile: +86 130 6268 8803

He's always offering to special order stuff, including tires, though I've not ordered anything yet.