I use a lot of Speed 400 motors in gliders, parkflyers, etc. And I break a lot of spinners on 6x3 folding props (mostly Graupner Cam). Does anyone know where I can buy replacement spinners(cones)? I know, learn to land properly.

I suggest you buy a model with a pusher prop, like a wingo or push-e-cat, until your landing skills improve. As far as I know, you cannot buy these parts alone. I also can't imagine how you're breaking them, as I've nosed-in a couple of times with these folding prop setups and have never damaged the spinner!
..a

Try this link, they have aluminum spinners. I hope they hold-up and shut the power down maybe 5 ft. before touchdown, might save a few bucks. Hope this helps

Yikes! here's the link http://www.aircraft-world.com/products.asp?id=62