Barry,
If I had to guess, I'd say 7-pin round. That's what I've seen on most 13-ers. Be aware that adapting from 4-pin-flat car to 7-pin-round trailer is kind of going "backwards." so for every ten places that carry adapters, only one will have
that one (ask me how I know).
There's nothing wrong with adapting that way (as long as you know that your trailer's
brakes,
refrigerator, and etc. won't work while you're towing -- and you probably don't even have trailer
brakes but I'm just saying), it's just that most people don't because it's "downgrading." That is, usually larger trailers with a 7-pin have
brakes, and so most people would also have a 7-pin on their vehicle.
When I picked up my
Boler I was faced with this same problem and I couldn't find the proper adapter anywhere (in Winnipeg). Luckily the counter person at Canadian Tire was a trailer person herself, and knew what I needed and directed me to a hitch place that made me one up in about 20 minutes ($17 Canadian).
Since then, I have found an adapter at Wal-Mart (although they are still rarer than the usual ones), so it is possible. Just don't be surprised when most of them go "the other way."
Congrats on your new Scamp!!

Have fun bringing her home!
Raya