Ebay is about the only place I can think of, besides finding a Dell authorized repair place nearby to see if they'll sell you one.
I did do some looking, and on NewEgg alone I came up with a number of cheap 92mm case fans. The 2.1A worries me a bit, because that is an awful lot of power to be channeling into a case fan.
Anyway, you can take a look at what's available. Just be kind of mindful of any the first week or so if you get one of these. If those 3-pin power connectors on your Dell system are pumping out 2.1A, when most of these are set to use less than a single amp, they may burn out pretty quickly. Still, you could buy about 10-12 of the cheaper ones listed on NewEgg for what someone wants for an exact replacement. It might also be useful to find one that has the same CFM (cubic feet per minute) rating, or higher, than the one you're replacing. There's at least one on there that is rated for over 100CFM, if you're willing to put up with the noise associated with it. Here's the link before I forget:
I have a Dell Dimension XPS with two cooling fans in the back. On one of the fans a blade cracked and broke off making it unbalanced and basically unusable.
The fan is a NMB 3615KL-04W-B86, 12V DC, 2.10A, 92mm x 38mm, 11" 3-wire cable with connector. I have searched all over for a replacement and can only find them for a minimum of 115$. Is there any other solution? Refurbishing? Substitute? It seems like a ton of money to fork out for a cooling fan. Thank you.