I hope this helps someone else out. I have been having trouble trying to find local steel fabricators for the past month. Someone on a Reddit thread told me to call up a local Airgas. Apparently, they are all over the place. The local Airgas will usually know of any local steel fabricators. Anyways, I found one nearby, called them up, and they pointed me to a welding and machine shop--I was Googling "steel fabricator" before. I called up the welding shop and asked about A36 grade carbon steel. I wanted to know if they had domestic sources, or any sources not from China or India, and how much it would cost. They said all of their steel are certified, and they have papers to prove it. They initially quoted me $52 for 14x16x1/2" of A36 steel including tax. However, when I got there, they only charged me $43 including tax because I was paying in cash. Ok, haha, lucky me!
I get the plate of steel, and holy moly, there is a THICK, oily amount of mill scale. It is pretty nasty. I asked the guy, "What's the best way to remove Mill Scale?" He said to get it sand blasted. He pointed me to a shop just down the street. I go there, talk to the guy, and he said it would cost $30 to get it sand blasted. I thought, damn, that really takes the cost savings out of this. But, oh well, better than trying to remove this extremely thick layer of mill scale. I don't know if all steel plates have as much scale mill as the plate I bought, but I already knew that there was no way a steel wire brush would get it off. So, I left it with the guy, waited, saw him suit up and take it into the blasting chamber. He comes out and asks, "Are you planning on painting on this?" I said, "No, why?" He said it's because if I paint on it, he won't take it all the way down to bare metal. I said, oh, you should. I plan on cooking on it. He said, ok, good to know. Then goes back and proceeds to blast it some more. In 20 minutes, he comes out with this unbelievably beautiful sheet of grey metal. I literally said, "WOW! That's an awesome transformation!" He said, make sure you season it with lots of oil. It will start to rust other wise. He was right too. When I got it back home 20 minutes away, it was already forming light areas of brown rust. Anyways, he said because it was so fast to do, he only charged me $10. SWEET! He also said with the amount of mill scale on there, it would have taken me a really long time to get it off with a steel brush.
Got home, and started to season the plate with shortening. Here are the before and after pics:http://i.imgur.com/UsmpsCF.jpg
After two coats of seasoninghttp://i.imgur.com/a04yRwJ.jpg
The thing is heavy. I weighed it on my scale and it's over 31 lbs. It also has INCREDIBLE thermal mass. I seasoned both it and my cast iron at the same time. Even after an hour of cooling, the cast iron was already cool to the touch whereas the steel plate was still registering 180+ degrees on the surface. Incredible.
Anyways, some thoughts. I know there are many threads on here about this stuff. In fact, I've been lurking/reading about them for the past several months. A few things I would like to add:
1) Skip the wire brush, vinegar, or any of that other garbage, and just go straight to industrial sand blasting. I have NEVER seen a piece of metal come out so RAW than I have with sand blasting. I've stripped cast iron in many different ways: oven cleaner, oven clean cycle, vinegar, sand paper, etc..., and nothing compares to what I just saw with industrial sand blasting. It is UNPARALLELED. Make sure you get decent quotes too.
2) I think you should definitely season a raw piece of steel. After 30-40 minutes of air exposure, my steel plate was noticeably browning. I've noticed this on my stripped cast iron pans before. To be fair, though, I do live along the coast line. Though, a few coats of seasoning shouldn't hurt.
3) If you're having problems finding a local supplier, try calling Airgas or any local welding and machine shops. They may know what direction to point you towards.
Hope this helps someone else out.