Parts are going to be very scarce. The product has been discontinued for a long time, but there may be a few places out there with some available - it's a matter of searching.
If the nozzles that are blocked are changing then it is probably not the head itself. It's either the ink (is it in date? Have you taken the carts out and given them a gentle shake?), or the duct or the damper or the wiper, or the broader cleaning assembly. Basically, it's either got an ink supply issue or a cleaning ability issue. Unfortunately, that could eventually lead to the head becoming permanently blocked so even if you get those other things sorted, you won't know for sure about the head until those other things are done.
Basically, though, I wouldn't be looking at a new head (if you can find one) without doing the other things first (which are cheaper, even though all together they add up a bit) because a new head will just suffer if the other parts are not working correctly.