Here's what I know:
There are two pure ukulele shops that I know of in HK:
1. Hong Kong Ukulele Service. I've actually never been to this one before (because they're all the way out in Sai Kung, and I think appointment based), so I'm not too familiar with their stock, but I know they carry a bunch of Hamanos, and they could order Kamakas for you - presumably from Japan - if you wanted one. (This info is kind of old, so I'd recommend checking out their facebook page and contacting the guy there directly. I really don't know too much about this store, but from the facebook page the guy seems quite passionate about ukuleles.)
2. ukehk.com They've been opened since spring last year, and recently moved to a new and more convenient location in HK in TST. They now carry Kalas, Ohanas, Eleukes, Honus, Mahalos, Makalas, and then maybe one or two Gstrings. They also carry a bunch of uke accessories - strings (worths, aquilas, hilos, etc), tuners, gig bags, stick on pickups, etc, and I think they've recently started some uke classes for adults and children as well. (so, yes, they are quite passionate about ukuleles too, which is always good to see.) I've purchased ukes and accessories from them, and they've always been very helpful. Definitely recommend checking this one out.
And yes, Tom Lee does carry a stray ukulele or two (usually Fender, which I didn't like when I tried it), and sometimes guitarleles (Yamaha) which are generally a bargain compared to the US prices. But it's more of a crapshoot as to whether the TL you're visiting will have any ukuleles.
As for other music stores. Again, crapshoot, some have them, most don't - but I did buy my first uke - an unbranded one - from a small music store in HK for about 10US about 2 years ago. It had horrible intonation and was more of a toy than an actual uke, but did pique my interest enough to find a proper uke to actually play from. But glad to hear that luckydog's is faring much better.
Pricing in general: I think certain models are a little cheaper than the US, but it really depends on the model. It is Hong Kong and not mainland China (where the factories actually are) we're talking about, so while they're generally on the cheap side and are very reasonable, don't expect some kind of crazy bargain. For example, A Makala Dolphin is about US$40. An Eleuke Mahogany tenor is about US$200. A Honu Tenor is about US$515. Pretty in sync/on the low end with US prices, though one good thing is that you won't have to pay 50 bucks or so for shipping.
Phew, that was a long post. Hope it helps!