[Leaked Stock ICS Firmwares] I9100XXLQ5 (4.0.4) - Europe (OXA) [04-07-12]
Base Firmware: I9100XXLQ5 (4.0.4)
I9100XXLQ5_I9100OXALQ5_OXA
Region: Europe
Country Open Europe
Carrier: Unbranded
Build Date: 28 June 2012
Modem: XXLQ5
CSC: OXALQ5
Change List: 753921

Source

Instructions For Flashing ICS:

Extract the firmware
Download Odin
Open the Odin
Put your device in Recovery MODE (Home + Volume up + Power)
Wipe Data/Factory reset
Wipe Cache
Take Out Your battery & put it back in
Put your device into Download MODE (Home + Volume Down + Power)
Click PDA and select I9100_CODE_I9100XXLQ5_CL753921_REV02_user_low_ship .tar.md5
Click PHONE and select MODEM_I9100XXLQ5_REV_02_CL1165929.tar.md5
Click CSC and select GT-I9100-MULTI-CSC-OXALQ5.tar.md5
Then finally click START!

I9100XXLQ5_I9100OXALQ5_OXA.part1
I9100XXLQ5_I9100OXALQ5_OXA.part2

or

I9100XXLQ5_I9100OXALQ5_OXA.part1
I9100XXLQ5_I9100OXALQ5_OXA.part2