Most auto parts suppliers or a shop that sells or installs trailer accessories or hitches should be able to set you up.
As for a name? I would just explain that you want to hook .... On your vehicle to .... On your trailer.
My question is are you planning on running from a 4 flat on your rover to 7 pin on a trailer?
If so are you aware that the basics 4 wire only works lights?
If the trailer is a 7 pin it is likely equipped with brakes and the 4 wire will not operate the brakes! Just so you know....
I got mine at Walmart or equivalent. Academy sports and outdoors, any parts store has it. I think seven pin to flat adapter is the name for it...that's what was on the packaging for the ones I bought. Make sure your pin numbers are right. I have a seven to flat with two different flats.