The smallest dual conversion RXs I've ever seen are FMA RXs. They make a 5, 6, and 8 channel. The 5 channel has the servo plugs on top, so it won't be as compact as the 6 or 8 channel, which has the plugs on the end...

[link=https://www.fmadirect.com/site/Detail.htm?item=1505&section=1]FMA M5 5 channel RX[/link]

[link=https://www.fmadirect.com/site/Detail.htm?item=1268&section=1]FMA Quantum 6 RX[/link]

[link=https://www.fmadirect.com/site/Detail.htm?item=1270&section=1]FMA Quantum 8 RX[/link]