I'm looking to build a Zero in 1/48 from a specific time and place but without the help of any pictures as none turn up in any search I tried.

The time and place is 2nd - 4th March 1943 Bismarck Sea, South West Pacific Area
Units that flew them is this battle were:
204, 252 and 253 air groups.

My questions: What mark of Zero would be correct? Which kit best meets the correct version and what were the markings for the units?

Thanks for any help

I think the easiest markings to find will be for the 204th Kokutai. They flew A6M3 22 Zekes and A6M3 32 Hamps. Here's the markings for the Hamp by Hasegawa. http://www.1999.co.jp/eng/image/10077715t2/60/2
You can also find the 204th Hamp markings in the Tamiya kit and Berna decals makes a set as well http://www.hannants.co.uk/product/BER48065

The markings for the other two groups are unclear. From Hata and Izawa's book Japanese Naval Aces and Fighter Units the codes were changed in September 1942, but there is no reference as to what those were. They just show what the codes became in September 1943.

So just go with the Hamp kit markings and you'll be alright. For the type 22 markings here's a reference from a flight sim game that gives you those 204th codes. Just scroll down to find them.
http://www.asisbiz.com/Zero.html

John thanks for that, I think I'll go with the Tamiya option.

I have read the books and watched the videos, I now have at least one of every allied aircraft type that took part with correct marking options (including a 1/48 Beaufort) I was just after a correct Zero I will also do an Oscar but that can wait a while.

Although a tender subject the shooting of the jap survivors is countered by the allied pilots witnessing downed crew being shoot and/or beheaded before this action took place.