Hi @Les I  welcome to this user to user discussion forum This is not Dell Support. 

The CPU and GPU fans are available for individual purchase [Here]. Guess that you are in the UK, internet search should reveal supply for the following new OEM Dell Part Numbers (DP/N):-
Alienware 17 R4 CPU Cooling Fan - Left Side - DP/N V613M
Alienware 17 R4 GPU Cooling Fan - Right Side - DP/N Y0DM6 

Thank you @crimsom I will give that a go.

Aware this is not Dell Support, was simply reaching out to the community to find out where we buy our replacement parts from.

Standard boiler plate disclaimer to be sure readers are aware, replies here are not from DELL.

Hi @Les I  thank you for sharing update. This is an English discussion forum and not specific to any country. The link in my earlier post is a US vendor that provides guaranteed New OEM Dell Parts with a one year warranty.  Internet search within the UK reveals Dell UK Parts Finder Tool, for Work or Home, but we have never used them. 

@crimsom​ is it difficult to replace the left fan that is making alot of grinding noises and then shuts off after awhile. I have a Alienware 17R4. Should I get Dell to fix my fan? 

Hi Ssherjj4  both the 17 R4 (9/30/2016) fans should be replaced. Please look at the following YouTube video Alienware 17 R4 Cooling Fans Replacement | Gaming Laptop.

It is a very tedious process that is NOT included in the Dell documentation, so be sure to have a basic knowledge of computer assembly before attempting. 

Advocate arrange for $100 Dell Laptop Repair | Dell Repair | Laptop Repair | Notebook Service Center (parts-people.com) Most repairs completed within 2 business days. All Dell laptop repair services include a One (1) Year Limited Warranty. This is by far the best repair solution.