Others here may have an answer - but those are tough lengths to find - very short and very long. RC Monster Mike right here could make some for you if you don't find them elsewhere:
mike@rc-monster.com
I've made a long dogbone here:
http://www.rc-monster.com/forum/show...t=26979&page=3
and others have done something similar with thick-walled steel tubes or by drilling aluminum or steel rod.