give ken a call, he should be able to get you an x4r frame, let us know how you go with it, I'm thinking about getting an x4r frame too Pitster Pro - Home
ken has x4r frames but when I called him he didn't have subframes to go with it.
You could possibly get a subframe from MoJo as the Pitpro XR's and Vert pro use a very similar frame
my 140XR frame has proved to quite strong so far, I've been jumping it with no worries, the jumps aren't that big but yea it holds up so far. If you haven't upgraded the forks yet then a set of GPX forks from DHZ would be a much wiser investment for strengthening the bike for jumps