The PNaCl bitcode wireformat and ABI is now stable and settled, as of PNaCl translator version "0.1.0.12180", and SDK version "Chrome 31 bundle. Chrome revision: 224887. NaCl revision: 12181". Anything newer should be backwards compatible.
Historically, this webpage was used to list translator and SDK versions that matched, as the ABI was still evolving. That is no longer necessary.
If you are still interested in downloading specific chrome snapshots with specific translator versions, you can check: https://commondatastorage.googleapis.com/chromium-browser-snapshots/.