If your device has Brocade direct maintenance support you can access the software via the Broadcom Customer Support Portal (CSP) at https://www.broadcom.com/mybroadcom/login. If your device has OEM entitlement/support you can access the software via your OEM or Partner.
The OEMs/partners have to check that you have a valid support contract. Their sites usually link to the Broadcom site and provide the software for you. If you're not able to find what you're looking for, you'll have to raise a support ticket with your OEM/partner or Brocade Direct support and they will help you get necessary firmware.There is some additional details around Brocade Direct Support as well as phone numbers to contact here: https://www.broadcom.com/support/fibre-channel-networking