Very good question!! As far as memory serves me, you might be able to get some from rcmart, or from Sam @ Kamikaze Toys and Hobbies.
I dont think they are supporting it any more since the rods are as good as paperweights
I still have only one spare left after I finish getting rid of my Evo3's pinch just around TDC, still can't turn it over by hand and it's got an extra 0.1mm shim in it. Secret of mine is that the piston is from my first Evo3 modified from AB Mods, and the sleeve is from a 2nd stock one I got. Perfect fit for each other, and I copied over the mod but added a little more timing to the Boost port.