I found it online, all C or P (domestic) on NWA and KLM; it may be cheaper if you book it through a consolidator. EWR seems to be the cheapest US destination. Unlimited stopovers. Try other destinations in the US and then Europe; the price will usually go up, sometimes significantly. Please share if you can find cheaper results.

Note: from a MR perspective, a RT BKK-EWR is a better bet, as it yields virtually the same amount of miles (~21,000 without fancy routings) for about $400 less.