From my point of view, the best way to find customers for rubber is to use Export Portal. Displacing your products in online catalog attracts international sellers and gives you the possibility to expand your business globally.
My advice for you is to use B2B feature on the website. It will help you to find your constant partners. Also, you can use "highlight" and "featured" opportunities, so as to make your product notable by the customers.
Btw, the top importers of rubber are China, USA, Malaysia, Japan and South Korea. More information here http://atlas.media.mit.edu/en/profile/sitc/2320/