CMF,
Maybe I am missing something from your question, but there are several coatings available for the coating of A36. The environment you are in, as well as, temperature and temperature fluctuations, final apprearance, fire-proofing, etc... determine the type of coating you may need.
I would suggest talking to some paint vendors. One I have used quite often is Tnemec. I have also used/specified Ameron products as well as Wilko products.
There are coatings out there, but more information on your final prodcut would need to be known.
Scott