I just had a look on taobao and if you type 5.25 into the search bar, then choose the first option (5.25转3.5), you'll find plenty of options for brackets. There's even a
simple bracket set for 2 yuan.
The link to the search page on taobao is: http://s.taobao.com/search?q=5.25%D7%AA3.5&keyword=&commend=all&ssid=s5-e&search_type=item&atype=&tracelog=&sourceId=tb.index&rt=1309480031549
The Chinese for bracket in this case seems to be 转换架.