I believe it is part number 42239, which are just the long bones, but in the shorter and necessary 42mm length. You will also need the full set of 42216 to complete the dcj.
I think you could also bypass getting the extra 44mm bones if you used 1x 42218 axles, 1x 42221 cross joint and 1x 42239 42mm bones, 1x 42220 bearings. This should save you about 20 bucks I think, as you aren't also buying the 44mm dcj bones which you will probably never use