I just found a website that has dictation subscriptions available. It's not too badly priced. For 4 weeks you can receive three dictations at your selected speed for $10.95 each. You can choose from Literary, Q&A (2-voice), Medical, or Names/Numbers. If you select the "special" 12-week subscription for $32.85, you can change your speed at any time. The speeds range from 50 to 225.
The literary collection usually consists of jury charge, general literary (essay or speech) or congressional material. The medical portion is reported to be medical minutes. It appears they are only available for speeds between 130 and 150 wpm.
I just thought I'd share. :)