You could pretty easily make one as long as you don't need to adjust height or tilt. If those are needed, you will need to make it more complex.
Seems to me you could just get a pair of chain link fence posts and a metal/wood plate. Drill 2 holes through each pole at the top and 4 into the plate. Then, attach your TV to that plate using the appropriate VESA spacing.
If you need it adjustable, you will need to make the plate attach with a clamping mechanism rather than bolts. If you need the TV to tilt, you will need to use a TV mount attached to the plate.