People order on Taobao now, so physical presence in a market is of dubious utility for many factories. The factories are mostly in Dongguan where they have their own component markets. The Baoshan area east and north of the airport also has industrial components markets (more process-line stuff). Huaqiangbei (HQB) is mostly consumer electronics with some components. There's more in Longhua / Longgang, northeast of town. China Post is super cheap for bulk shipping if you choose surface (ie. sea freight) but it takes three months.