Where to buy metal grills for custom cabinet door?

Good morning.

I am moving into a new condo and am building a semi-custom cabinet setup for my audio equipment. I'll be buying some used normal cabinets, removing the doors and building the new ones. I would like to use the metal grate-style doors that allow heat exchange but still hide most of the inside.

Any ideas about how I can DIY these doors, ie, where can I buy the metal grate style inserts? (think "Salamander" equipment doors, but a lot cheaper. For a specific example, google "salamander style 221.").

Any and all help is much appreciated.