James,
As AlexandrP mentioned, you need a Summit X670 switch (either X670-48x, X670V-48x or X670-G2-48x-4q) with 12 10/100/1000Base-T SFP transceivers (these will only operate at 1G). This is a 48-port switch, so you will have an additional 24 SFP+ ports, but is the only one that will give you the port combination you need.