Convekta's CT-Art (I have version 4.0) is graded in the way you seek. You can do tactics by theme (e.g., forks, pins, etc.) or by difficulty (level 10 of any theme, then level 20, etc.). Some of the tactics are very difficult though. I haven't made it past level 50 yet, and they go up to 90 in steps of 10, but the initial levels are easy, though still worthwhile to get the patterns really ingrained in your memory.
Sounds interesting enough, and I believe it's part of a bigger package or some kind, 4 or 5 volumes maybe,
Almost the same DarkJedi, you have done 116.3 hours, I've done 116.6.