i need some steel for my knifemaking stuff.
I've made several knives out of old files. You can often find them at garage sales.
I have a friend who found a good source of metal great for homemade knives. A local Lawn Mower shop had spare/dull "bush-whacker" mowing blades. They start at a nice thickness, and he free hands several knife "blanks" from just one mower blade with a portable oxygen/acetylene torch. From there its just grinding/filing/polishing until you're satisfied.
like rich_moe said, leaf springs work the best, just straighten and temper them.
Check your local junkyard for leaf springs and chrome bumpers from older cars/trucks. I've had good luck with that.
If you're after scrap check with your local recycler, or industrial supplier, or even a junk yard. If there's a specific quality alloy you're after you could try OnlineMetals.com http://www.onlinemetals.com/You can order just about any type of metal, and you can select your size and thickness. Hope this helps!
check out a local metal recycler. They will have all kinds of metal and if it's a small piece they may just say take it it.
Look in your yellow pages under metals, or call a local metal working shop and ask them.