I saw a dom in Ottawa, who had a U-shaped cage made from metal tubes connected with railing fasteners (which were tighten to the metal tubing/piping by allen screws).
Kee Clamps?
https://www.keesafety.ca/products/kee_klamp
Also check amazon for prices.
It could hang a sex swing or head stocks, depending on how you wanted it designed.
The thing is you need to design it with load in mind. The distance between supports for something that hangs from the frame. At a span of 8ft (assuming a u shaped frame 8 ft per side), use min of 1.25" Inside diameter sch 40 pipe (1.7" Outside diameter). using fig 1, the limit is 562lb.
Most people are say 200lbs, so 2 people is about 400lbs. So if you have a swing with 4 holding points, and 4 legs on the ground, thats about 100 lb per leg. Pls note that I am assuming that the sex swing will hold 2 people.
http://www.alvinindustrial.com/info/info_02.htm
You could have sliding bars to adjust for height and distance someone would have to bend over (90 degrees) to be in an head stock.
The thing is cut the pipe to length and put into the fittings to form the shape you want. Its also portable/able to break down.
Thing is its costly for the steel and fittings.
Or you could make a bench using smaller pipes. Using 3/4 inch pipe for the frame, and with plywood backed vinyl bench seat.