I had to do this once for a P-No. 1 base metal and wound up reviewing material specs to determine which specs would be likely to allow a chemistry range that would produce the CE we needed to qualify.  Ours was only about 0.50, and I think we wound up using A675 bar stock machined into pipe coupons.  We worked with several steel companies to review potential MTRs that might work till we found one.  Once you have a list of candidate specs, you might try contacting Federal Steel Supply to see what they can find for you.  Their number is 800-325-1584.