Check eBay, there are some on there or just go to Home Depot or Lowe’s, buy a 2’ length of 2” wide aluminum flat bar.
Bend one up for the width of the unit, drill holes for mounting knobs and to mount bracket horizontal.
If you don’t have the 2 knobs, think they are 6mm thread and short bolts & washers will work.
Spray can black and no one will know the difference.
Probably $10-$15 out of your pocket and 1/2 hr labor.