It's made for BMX bars, which are 22.2 mm diameter, slightly smaller than the running length on Nitto bars. Nitto's are a road standard dimension, so regular road levers (or any lever sized for road bars) will work. I haven't seen a Dirty Harry in a road size, but you can get Goldfingers in both sizes (actually in 22.2 and then a 26.0 version with shims supplied to fit the Nitto). The Goldfingers are very hard to find in the larger size, for some unknown reason. I have an extra couple levers if you want to buy a pair and trade off the other one to someone else; PM me if you're interested.
By the way, this is the same problem with Paul levers. An option to consider (not quite as short as the Dirty Harry) is a cyclocross top-bar lever -- everyone makes them and they work well. They actually have better leverage with regular dual-pivot road brakes.