If I don't want to use a spine tester (or can't use one) to get me in the ballpark, I choose a shaft that looks way too stiff, cut it to the proper length for my draw, sharpen the tip, cut a nock into the other end (the smaller end), and shoot it at a target about 10 feet away. If the nock end leans to the right, the arrow is too stiff (this applies only if you are holding the bow with your left hand...the opposite happens with the right), and needs to be made thinner......or another, thinner shaft need to be chosen.
I do this until I find a shaft that shoots straight into the target. I repeat with the next, etc., one until I have several shafts that shoot straight. Then I divide them into groups of similar weight.
With natural material the spines and weights can vary quite a bit even though they may look similar in diameter. Trial and error is the only way to pick shafts that shoot well, IMO. If you order shafting from someone else, it's always best if they have been matched by shooting....in addition to being matched by length, material, spine, and mass.
With river cane shoots, it's not always possible to shave them down and make them thinner (like you can with hardwood shoots). After you find one that shoots straight, you'll need to find a way to measure how stiff the spine is (so you can make duplicates of your good arrow). Some people can do this by simply bending the shafts in their hands. If you can't feel the spine, then you'll have to come up with some kind of contraption to measure the deflection.
Hope that helps.