Go to www.dell.com/drivers and choose the wanted system type by entering the Service Tag or selecting the product type manually.
Select an operating system and enter "MIB" in the Keyword field.
Now the corresponding MIB package is shown below. Click on the download sign to receive the package as a .zip file.
Figure 1: Download MIBs
The OpenManage Server Administrator also has MIBs located in the support folder.