Last time I was over in china, which was just days ago,  I managed to go by the Kenda company and complain about the lack of  20" tubes and tires ..   Kenda is the underlying manufacturer for the summit brand we sell here in the states.     One of the things I complained about most loudly is not having a decent small sized 20" tube.. you know .. like a 20x1 with a nice long presta stem  ---  Well it turns out they actually make one (yay!), but the summit people don't distribute them in the US. (boo!)
 
However, they are willing to sell me as many as I want to take home with me next time I'm over there, as long as its an order larger than 36 at a time..    I was even able to acquire a couple of them as samples to try out .. but presuming they go round and round like any other tube, I'm going to bring some home next time .. which brings me to RBENT ..  
 
My costs is going to be about $3-4 USD each for these things, not including the suitcase to carry them home.      I should be going back over there in August, or September at the latest.   Let me know if you want one, or 20  and I'll put your name on a box.. these will be 406s with 32mm stems, like the ones in the picture below