mjalkut,
You won't find such product for the simple reason that its potential users for the Z are less than a hundred. The companies that produce mapping applications for other PDAs are not interested. Independent developers cannot afford to license good map databases. I checked -- even if I create the software for free, with such a small user base, the cost for the end user would be hundreds of dollars (let me guess how many of you would buy it for that price
You make some good points but there is also another way to look at this.
Linux in general is certainly popular enough at this point that someone should
think about producing a full commercial GPS+maps package for it (if it does not already exist).
Once that is available, it should be easy to port it to Z (so whoever
does this comercially would mostly make money selling to people who use
linux on laptops and zaurus version would require little extra work/support).
Of course some will now argue that even on laptops there may not
currently be enough interest for this, but at least there is no doubt that
linux will survive on laptops (as opposed to Zaurus where it's anyone's
guess what if anything Sharp will do in the future).
I also happen to think that due to similarities of Linux to BSD, any GPS package developed for linux should be easy to port to OS X (and vice versa) and then you have enough users
between Apply and Linux comunities (of course same should be true for Adobe
Photoshop which runs great on OS X but Adobe does not want to produce Linux version
which I'm convinced would sell great).