Trade was my original source of iron. When asking for specific trade goods, don't just ask for bars. Ask for other items suitable for melting, like anvils. One trade caravan can boost your iron stocks up quite a bit if you diversify your selection of iron goods. Maybe you've already done this, but I didn't when I first started out.
Yeah, I did that a few forts back. This fort is young enough that it didn't seem like a good idea yet.
Besides, I have other things going on, like this:
It's a forgotten beast in a cage! ...well, not an actual cage, but you understand what I mean. I have plenty of space on either side to set up magma or water or both. I can even release it more or less safely with hatches as bait to control its movement. This one has deadly blood, so it's not likely to ever see the outside of its cell, but if others come with less fearful attributes, I may use them for live training, once I think my military is up to the task.
My system worked mostly perfectly. A few problems arose, such as my leverdwarf sleeping on the job, but once he was in the airlock, it was just a matter of time. I had to rebuild a hatch after all was said and done, but that's going to be more or less standard operating procedure. The only vulnerability is time - if another beast shows up directly after the first one, and I'm not taking the time to airlock dwarves in and out, then I could lose a few to them. But it's not very likely. And besides, who am I to completely rule out the possibility of fun?