I know that I've seen stats for transports somewhere. Most races can be 'rationally' done though.
IN/SM/Chaos/Orks/Tau:
All these fleets have similar enough stats that rationally you can use the same 'standard' transport stats. Orks obviously would use stolen Imperial ones, (some people use 6+/4+ armor instead), chaos uses imperial stylings as well.
Forgeworld obviously has stats for the tau ones, but I never thought that unique stats for their transports were necessary. Honestly in the interest of fairness it is easier to just use the 'standard' ones.
Tyranids would need stats written for theirs comparable to 'standard' transports, and they would need a modification to the 'hive mind imperative' table to make them more appropriate (i.e. running from threats rather than trying to eat them).
Necrons could simply use a modified 'standard' vessel, likely one with some rule preventing it from using AAF, at least to its fullest extent, or perhaps limiting its ability to produce AP etc.
Eldar/De have stats somewhere, and these are decent, never had any issues with either. Given the 'MSM' versions are a bit annoying, I've never lost a game with Orks vs. MSM Eldar who had to get somewhere (MSM vessels are weak when they MUST be out in the open).