I know that this Topic is very old, but I was facing the same issue.

The solution is:

Connect via CLI (SSH) to WLC and type "debug fastpath cfgtool --dump.sfp"
you dont need to type "FP0.", thats part of the output

I censored the output with XXXXXX:

(Cisco Controller) >debug fastpath cfgtool --dump.sfp

(Cisco Controller) >FP0.
Port SFP Vendor       Transceiver Type    OUI PartNumber       Rev  SerialNumber     DateCode Auth
   1 OEM              (0x01)1000BaseSX        GLC-SX-MM-G-UL   2.0  VB11XXXXXX      110701   ok      
   2 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   3 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   4 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   5 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   6 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   7 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
   8 Not Present      (0x00)NOT_SUPPORTED                                                     fail    
FP0.

hope that helps someone for the next time

Probably a little late but via GUI [Controller] [Inventory]

44020 version 7.0.240.0

I thought you might be on to something ... but just checked my 4402 and no love ...

I dont think you can get the serial from an SFP on a WLC

Awwww nuts! 

sh inventory.

Right you are !!!

Thank you !!!

If it works, can you please rate my post?  Thanks. 

Yes, sure.

Five stars !!

Thank's for your help ! It's very useful !

Peter,

What WLC and Code version are you on!? I checked gain on 2 different WLC running 6x and 4x and both arent showing the SFP info...

(Cisco Controller) >show inventory

Burned-in MAC Address............................ XXXXXXXXXXXX
Crypto Accelerator 1............................. Absent
Crypto Accelerator 2............................. Absent
Power Supply 1................................... Absent
Power Supply 2................................... Present, OK
NAME: "Chassis"    , DESCR: "4400 Series WLAN Controller:25 APs"
PID: AIR-WLC4402-25-K9,  VID: V01,  SN: XXXXXXXXXXX <--- This serial number is of the controller

(Cisco Controller) >

Hi there!

Any update on this topic?