Velcro would make them stick together but they'd wiggle and flop around, rather than being one solid piece. Once I see the model in split and combined forms, then I can start devising. Also, a guesstimate on the lengths of them would help for accuracy.
I wish I knew how to do that kinda stuff...I would totally make it for you! And a perfect way to have it so it can go from one to two blades, just have magnets in the middle...
My specific method of making them is a challenge itself, making them safe to play with and at the same time staying accurate to the design. I think I'll have three concealable points of PVC on either blade to connect them together, but any ideas are open.