Yes, I've tried to look for those but haven't found a match. There's the dubro brand but they are too long. perhaps they can be made to fit, not sure.

The sprint 1 had the captured ball ends, take a look at the picture I posted. Beautiful system with virtually no play in them. Unfortunately those have been discontinued a long time ago.

best thing I like about the sprint2 is the worry free transmission due to the steel gears in the differentials. I don't have a lot of time to wrench on the cars so this is a big plus for me.

By the way, another thing to keep in mind: you can put in differential oil to replace the grease in the diff box. this will make a smoother diff. On the front diff i use a very heavy diff oil (almost like clay) this makes the diff behave almost like it's locked but still allows some diff action.
If you put diff oil make sure your sprint comes with the small o-rings meant for the diff boxes (there should be a total of 3 o-rings for each diff case: 1 large and 2 small ones). I think on some RTRs the small ones are not installed, so it is important to check that otherwise the diff oil will leak.
Part# is HPI 86016 , that one comes with all o-rings for the 2 diff cases.