Well, to start with, 3x3 uses the same length spokes as a conventional 3-cross wheel, so any spoke calculator should be able to do that.
As for resources, have a look at
this, it's the only information I've ever found online about exotic lacing. You may already have seen it, but it does show how to interlace the spokes on a 3x3 wheel. It also explains how the guy who wrote it works out the spoke lengths for his wheels.
The first wheel I ever built was 3x3, so my advice is just do it and pay attention to the over/under lacing, I didn't the first time, and as a result I ended up having to remove and re-insert a load of spokes.
As I recall, it can be a bit difficult to put the spokes into one flange once the other side is laced, particularly the ones with the heads on the outside. As such, I'd suggest putting all the spokes (or at least the ones with the heads outside) into the hub before you do any lacing, and be careful not to "trap" any of them in the gaps between all the spokes in each 3x3 group as you lace the first side.
That may well seem like a load of gibberish now, but it's the best explanation I can manage. Once you start building the wheels, it will hopefully make more sense.