If you have no access it s hard for me to tell you to go to extremes to find a way.
Do you need to ground antenna in attic.
Antennas mine are receive only for fm tv and public safety bands will be generally restricted to the attic.
For all practical purposes an attic antenna is considered and indoor antenna and does not require any special grounding.
The nec requires that the antenna mast be grounded directly.
If you ve taken the time to insulate lay flooring or even decorate your attic however you may want something that s a little less of an eyesore.
If you find the attic install unsatisfactory and you move the antenna outside then you definitely do need it.
Some attics are dark unwelcoming places used only for extra storage and in those cases nearly any antenna will get the job done.
But if you have access to a ground connection that can serve the attic splitter it makes sense to use it.
If you look at the image below you ll want to use a 6 awg ground wire for all of your grounding runs and suitable ground clamps.
Keep your grounding parts however.
Agreeing with adtech i don t see the nec requiring you to ground an indoor antenna system.
However the connection of your antenna coax to various ac operated equipment in this case your converter box or tv introduces the potential of electric shock.
Typically the house wiring and gutters represent a much lower impedance path to ground for lightning than the floating attic antenna.