First of all BridgerNY, welcome to AR15.com. It's good to see more New Yorkers here. As for New York law, any semi-automatic rifle that is legal at the federal level is legal at the state level. Meaning, according to NYS, you can order as many post-ban Bushmasters or Armalites as your heart desires. Not only that, but you can buy as many pre-ban 20/30 round magazines for those rifles as you want too. That dealer you spoke with is a dope... which doesn't surprise me as I don't have a very high opinion of FFL dealers (may apologies to you good FFL's), most I've dealt with are a level or two BELOW a used car salesman. Most dealers don't know their asses from their elbows when it comes to "assault weapons" and you should always keep that in mind when dealing with them. It is completely fine to use a pre-ban, over-10 round magazine in either a pre-ban or post-ban AR (or AK, FAL, etc.).
Get the black rifle. You love it and it won't be your last. Hope this helped some.
BMAN