Try U Haul. They list adapters specifically for several German makes but not speciofically Volvo. My guess is that the Volvo is compatible with the German makes although U Haul doesn't specifically list Volvo on the chart. Where in Missouri are you? If you are around the Kansas CIty area Croft Trai...

My 850 Estate has the factory Volvo receiver hitch, as well as the factory 7 pin round plug for the trailer lights. I've managed to rig a working method of adapting the hitch so it'll work with a standard class 3 trailer hitch, but simply cannot find the correct 7 to 4 adapter so I can plug in the t...