With the Analysis ToolPak add-in activated (tools-addins):
Cell address in range A1:Z1000
=ADDRESS(RANDBETWEEN(1,1000),RANDBETWEEN(1,26),4)
Press F9 to generate a new random address.
If you want the contents of that cell:
=INDIRECT(ADDRESS(RANDBETWEEN(1,1000),RANDBETWEEN(1,26),4))