Check with Chickeeduck (a baby clothing store), Jusco and Yata department. They should have it. A few wet market streets in centeral also have it as I remember some mothers mentioned it in the forum.
From Jusco, I bought a few gowns that is open in the front with snaps.
Gowns are convinent at the begining for diaper changes. Newborns are mostly wraped in blankets and go through so many diapers a day. When you wear baby in gowns, you just have to upwrap the baby and pull up the gown for diaper changes. Then you pull the gown back down and warp baby up again. No need to put snap back under the crotch. When I think the baby needs another layer, I would add a vest for him on top of the gown.
Footed pajamas are great for holding the baby. So, his clothes are not all pull up. With gowns, after holding the baby for a while, his gown could all be up in his tummy. I found that we have to tidy it up for a bit.
But when the baby is screaming for not liking dipaer change, I don't like that i have so many snaps to put back to dress him again. Somehow, My helper and I often snapped it the wrong button, and then we have to go through it again.
I am a bit long-winded here. Like shenzhenier, many mothers don't mind the over the head onesie. It really depends on if you are used to it. I guess.