Probably there are also other links, but I cannot find them. As written the pass rate is quite low (less than 50%), but also unsuccessful stories can help very much.
Maybe an improvement can be put in the feedback of people that have not pass the interview to explain more how and where the candidate can improve. There are some indication of area that must be improved, but maybe too much generic.
Blogs are not the primary sources of information of VCDX paths.
There is also the VMware community (but seems not too much active on VCDX area), twitter (I think that could be must, for example to find other candidates in the same period) and more important a direct iteraction with people that are in same boat or that have already had this experience (and events like VMworld could be a good chance to meet them).
Note that NDR do not permit at VCDX or previous candidate to talk about the questions or the design details, but seems to be permited (as written also in the official Defense Prep) that a VCDX make a review of your design ("Consider that VCDX-certified architects are reviewing your application" is the exact sentence).