Have you tried your local timber merchants and asked about round fence posts, I have cut the pointed ends off and they are still long enough(especially when used in a small school)They are pressure treated so dont rot and are nice and heavy. My young daughter enjoys painting them in the summer holidays(use masonary paint).
I buy 10 ft round poles from my local builders merchants and paint or stain. I also have a couple of brown plastic soil pipes thayt I use for skinny jumps, you have to be careful if using plastic pipes that they are not too brittle
A free option for you......
Carpet shops often struggle to get rid of the long tubes that carpets come on! Years ago a few of the companies used to use plastic tubes which were fab, but now i would say 99% are thick cardboard. But... as long as you keep them inside when not using them, and dont try and use them when it's windy - they are great and can last months on end.
Happy Jumping!