Contact the GPU Manufacturer Support and see if they sell the GPU Cowl (covering with heatsink and Fan). If it was under Warranty, when you removed the Cowl, you most likely voided the Warranty on the card.
Google R9-390 Fans. There are many places that sell replacement Cowls and Fans for your GPU.
Have you thought it might not be the FANS at fault, but maybe either a driver issues or PSU or Motherboard issue or the GPU card it self ?
I googled "R9-390 Fans not spinning" and got many threads. Most seemed to have found a solution. Try it and look at some of the solutions on several of the Forums on Google Search.
For more help you need to give all your computer information according to AMD Forum's rules: IMPORTANT: PLEASE READ BEFORE POSTING