You would need to have a valid support contract with Mellanox Technologies in order to get the software image.
I'm in the same situation. I bought an HP c7000 off of eBay that came with a managed FDR switch for my homelab. I can't do anything with it because everything I do, I get the "no licenses installed" message. Does Mellanox offer any type of homelab or non-commercial licenses for people that want to learn their technology? The only way I to run it now is to run OpenSM on node connected to the switch. It would be nice to be able to play around with the managed switch.
The HP switch blade software are licenses are provided by HP. Did you try contacting HP for servicing the equipment?