Go to your local carpet store or any store that sells rugs (usually stores that order them for you, not somewhere that just has rugs in stock, also small family owned stores work better for this) and ask them if they would put aside their carpet samples for you when they become discontinued. Usually places will do this for free because the employees don't really want to take them home and might feel bad about throwing them out like I used to.
Once you have all your various samples, you can lay them out in the way that you want to create your rug. Grab some carpet tape and a friend and you will have a fabulous original rug in a few short hours!
Hint: you can also ask them to put aside discontinued upholstery samples, linen samples etc to use in other fun recycled projects! Sometimes upholstery samples are actually big enough to recover a stool or kitchen chair!