Need help finding a replacement motherboard for Alienware Aurora 875 chassis

Hi

This is my first post as I am new to the forum so if it is in the wrong place I apologise.

I bought an Alienware Aurora about 2 years ago now and after 16 months the motherboard died. After many unsuccessful attempts Dell were unable to supply a replacement. The first motherboard they sent did not work, the second was incompatible and I eventually gave up after 6 months of frustrating correspondence. Dell informed me that it was a special edition and that they were not able to source a replacement part because of this. I was staggered to say the least that a company was not able to locate a replacement part for one of it's own computer sold 16 months previous. 

What I would like to ask if can anyone kindly direct me to or recommend where I can purchase a suitable replacement motherboard from, the rest of the computer is fine and I really would like to get it up and running again rather than having a very large £950 doorstop.

Any help or advice would be greatly appreciated, thanks.

210-38735 Alienware Aurora : Matte Black 875W Chassis 1 ZR

203-33147 D00AMW01 1 ZR

213-15454 Processor : Intel Core i7-3820 (Four Core, 10MB Cache) 3.60GHz 1 ZR

340-30867 Resource DVD : Alienware Aurora W8 1 ZR

370-21940 Memory : 16384MB (4x4GB) 1600MHz DDR3 Quad Channel 1 ZR

400-24047 Hard Drive : 1TB SATA 6Gb/s (7200RPM) 32MB Cache 1 ZR

412-AABI Heatsink : Alienware CPU Liquid Cooling 1 ZR

429-16628 Optical Drive : DVD+/-RW (Read/Write) 24x 1 ZR

450-17803 Power Cord : UK 250V 1 ZR

490-14169 Graphics : 2GB GDDR5 AMD Radeon HD7870 1 ZR

510-10439 Sound : Integrated HDA 7.1 Dolby Digital capability 1 ZR

545-10006 Gaming Software : Steam Gaming forum and download application 1 ZR

580-17753 Keyboard : UK/Irish (QWERTY) Alienware Multimedia Keyboard 1 ZR

619-38324 Operating System : Windows 8 64bit, English 1 ZR

620-13846 Os Media : Windows 8 64bit, MUI Resource DVD 1 ZR

640-13025 Software : Dell Backup And Recovery - Basic 1 ZR

644-10057 Avatar : Avatar not included 1 ZR

650-13313 Antivirus Software Not included 1 ZR

656-10005 AlienFX Colour : Quasar Blue 1 ZR

754-56830 No Warranty Upgrade 1 ZR

754-56829 Standard Service - 1 year of Next Business Day coverage included with your PC 1 ZR

755-10605 No Accidental Damage Protection 1 ZR

799-17924 Alienware Aurora Order 1 ZR