I pasted your Chinese name in a search box. It returned pages of Hydrocotyle vulgaris, common name marsh pennywort. I don't know where you can purchase it though. http://en.wikipedia.org/wiki/Hydrocotyle_vulgaris
Well, not that one then. A search returns quite a few pages on tongqiancao, but as with any common name, it has several meanings. Can't track anything down that looks like that and has any real plant name attached to it. This page show a plant that looks right, but no name (that I can find using online translator.) Although if the flowers are right that might help someone ID it. http://mail.lsps.tp.edu.tw/~edith/newfile148.html Maybe a local Chinese herbalist would know the plant. Ron is probably correct, some images of Centella asiatica look like the plant.
http://en.wikipedia.org/wiki/Hydrocotyle_umbellata ? Appears to be native to Nova Scotia http://plants.usda.gov/java/profile?symbol=HYUM&photoID=hyum_2h.jpg Possible Supplier http://www.wildflower.org/suppliers/show.php?id=3796
The photo in the original post looks more like the water pennywort, that's why I said "supposed". Maybe one is being shown in place of the other, by mistake.
Hydrocotyle asiatica is a synonym of Centella asiatica. http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200015478 There are 20 lower taxa of Hydrocotyle native to China. http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=115990 Both Centella asiatica and the Hydrocotyle have orbicular or reniform leaves. The photos of both online are quite varied and I have not found any associated with a reputable botanical site. This is beyond my training, but I am intrigued to know the correct ID. I was thinking Centella asiatica seems like a plant that one would be likely to encounter in China.
Water pennywort is a nuisance plant is this region, covering the entire surfaces of quiet waterways like ponds.
This is a rather old thread but in case you're still looking, Hydrocotyle vulgaris is available at Southlands Nursery - Home.