I don't know of MCX versions, but SMA versions are fairly plentiful and BNC 10dB attenuators are fairly available too. I'd look for a combination of an MCX to SMA/BNC adapter and then one of the more standard attenuator formats.
I do see one minicircuits MCX attenuator on ebay, only 4dB though, so they are probably available as custom order from them, but I imagine not cheaply.