You should try Candybar. If you don't want to pay for the software, I have an alternative. Download Candybar Version 3.2 [ONLY]. Use the unregistered demo.
Once downloaded, Open Candybar. Once it is open, Look at the top right of the window. You should see 14 days remaining. This is because you are not registered. To register for an unlimited time, download the attached plist preference file I have attached.
Once downloaded, open the zip. Copy the plist file inside and paste it in Library>Preferences. Select Replace.
Now open candybar and it is registered. You may now import unlimited icons and have unlimited time for free. Hope this helps!