Download VirtualBox Image (IOS) of Juniper Router for GNS3:From here you can download "JunOS Olive 12.1" VM image, you can run it with GNS3 for simulating juniper router. (Please note that this image is only provide to you for informational purpose and for GNS3 use.)
What is JunOS Olive?
JunOS Olive is a software that you can use on PC. Initially Olive was used by Juniper internally for lab work, but now it become a source to learn the JUNOS CLI on a low-cost platform. Please note Junos olive is only for study and practice purposes , which is unsupported and unsupportable platform & it is not suitable for any type of commercial use.Download JunOS forGNS3:
You can actually run this JunOS on VirtualBox and then can simulate this into GNS3. You can Download this JunOS for Gns3 from following link and can perform and configure different lab on Gns3.
Download JunOS olive Gns3
Click on above link and then choose "download anyway" for download this file.