When you say c.r. low carbon steel, are you thinking 1010, etc... are corrosion reisistant? That class of steel is definitely not corrosion resistant.
If you are looking for relatively small sizes and/or non-complex shapes, you can get some through McMaster-Carr (www.mcmaster.com).
If you are wanting some large or custom pieces, you'll need to find some place that reps for a mill that is relatively local to you unless you want to pay shipping. I know quite a few places around me, but I doubt that that would help you. What city are you in?
The corrosion is not an issue, I've tried all the sites you listed with no luck, I'am looking for 5/16" rod and 5/16"x3/8" rect. As well as 3/16"x3" rect. and 1/4"x3/4" rect. I live in Wilmington N.C I've tried local steel suppliers and they can't help me, and keep sending me around in circles. If the price is right shipping does not concern me.
I see why you're having issues. You won't find standard mill runs in those sizes. You'll need some machining if those are hard and fast dimensions you have to have. Can you give the overall lengths as well?
I've dealt with a few local machine shops as well, seeing if they had access to the grades I'am looking for with no luck. The machining I do myself. I don't need specific parts machined. I just need the dimensions that I stated in any particular length. Usally I buy my other metals by the ft. In any case dimensions close would be adequate so I don't have a ton of work to do thanks.
The round stock is the right grade, but galvanized which is no good for my application. 1018 is what I use for all my dimensions already. I would be happy w/ 5/16 rod & 5/16x3/8rect in 1010 or lower. I use this material for elctromagnets and armatures. Not solenoids, but a soild core electromagnet with an oscillating armature. Basically an old fashioned doorbell circuit. I appreciate the help very much, thanks.