I buy all my new specialty steels from a company in Palatine Illinois - called Admiral Steel. They carry all types, but do sell small quantities of the most poplular steels used by knife makers. They are a huge wholesale/wharehouse supplier of steel, but have carved out a small part of the market for Knife Makers. So they can and will sell you small quantities of any of the knife-making steels. Their web site is something like admiralsteelonline.com - but a web search should bring it up. Be sure to tell them that you are a Knife Maker when you contact them, otherwise they will think that you are just another machine shop - and price accordingly.
Oops - missed the post below with the link to Admiral Steel. Just make sure you tell them that you are a Knife Maker.
But if you just want some new (or used) steel to start playing around with, get ahold of some Lawn Mower Blades. They are generally 1085 carbon steel, or 5160 alloy steel. Both are good for knife making - and pretty cheap. If you search through the blades, you will find several different thicknesses, and a variety of widths. But most are at least 2 inches wide, and 3/16 inches thick.
Also check out some of the farm implement parts at a store like Farm Fleet. The bolt-on replacement Plow Shares and cultivator points are generally 1080 carbon steel. So are the "knives" for the big rotary mowers. And the replacement tines/teeth for the hay rakes are either 1080 or 1095 spring/tool carbon steel. I use the hay rake teeth to make some flint strikers out of. One tooth runs around $1.09 at the local Farm Fleet store, and I end up with about 3 feet of 1/4 inch round rod by the time I straighten it all out.
I prefer to use NEW steel, either bought from Admiral Steel or from the farm store - because some used steel can have hidden flaws/cracks/memory in it. I've heard numerous stories of people making a knife blade out of an old vehicle leaf spring only to have it always warp back to that original curve it had. Sometimes you just can't correct that built up "memory" in used steel. I also had a coil spring from a small trailer that would develop a split all along it when I tried forging it. That split showed up in almost every part of that used spring. So now I prefer to start with new steel. Altho, I haven't had any problems using old lawn mower blades - so far.
Good luck on your quest for Steel.
Mikey - out in the Hinterlands of the upper Midwest