Hard to find? Depends. Yes, if you are looking for birds that carry type similar to Blacks, Whites, Buffs etc. There are a couple hatcheries that offer them so that's a possible source. Just don't expect the quality of exhibition Blacks, Whites, Buffs, etc.
As herechickchick stated, I am working on them, but am not ready to let any go just yet. I am on the f3 generation and hatched around 40 splits to Black this spring. We'll see how they look in the fall. I am hoping to have good representative Self-Blues in the f4 generation. Again, we'll see. At any rate I plan to raise around 50 next year, which means I'll need to actually hatch 200+ since 75% will be black chicks, either pure for black, or splits. Since you can't tell which is which, none of those will be kept.
Lots of issues to deal with in developing these. Leg color on the original pair was incorrect, as it is with most of what you'll find out there. Ear lobe color is poor, feather quality isn't great, which seems to be an inherent issue with the color as a whole, and the type was terrible. However, the f2 Self Blues that I used for the f3 generation at least look like Cochins!