Here in the UK, getting your hands on any tretinoin is a complete nightmare! Our only topical prescription containing tretinoin is Aknemycin Plus which is a solution in alcohol (very irritating) and it also contains erythromycin.
We have no access to any medications such as retin-a micro or ziana etc. We used to have a product called Retin-A which was just tretinoin in a gel and then in October 2012 it was discontinued! I have been using differin but it just isn't quite strong enough.
Anyway, I have started a group of facebook to try and get a few of us together who want retin-a back! Come join me!