Like davenn says, a lot of electronics and big-box stores sell the converters. They
were marketed heavily when the U.S. changed the standard for local television station
broadcasts from analog to digital signal. Ask in a store that sells televisions, they'll
know what you're talking about. The U.S. government gave out free $40 coupons when
this all happened, to help defray the cost to people who had the old TV sets, which
jacked the store price up to $80, so they could make money off the coupons, and
customers. Most anybody who needed one back then, got one, so I would HOPE
the price has come down since then, because I don't imagine there's a big demand
for them now. I got a few of them to test out, worst one I found was made by APEX.
I'd avoid that brand if I was you.
I don't know how dish/direct tv works. Just call them and ask them on your old Zenith.
Cable companies were not affected by the 'over-the-airwaves' broadcast standard change
from analog to digital, their signals to your TV did not change. All of my televisions in
the house are on cable, they're all the old analog TV's, and when the local airwave
stations went digital, the cable company signal to my old analog TV's was completely
unaffected.
Sorry to be the bearer of bad news on your Zenith. I know you want to keep the legacy
going. The Zenith sets were a pleasure to repair, but everything is dependent on
seeing the picture on the picture tube, and I don't know anybody that rebuilds them
anymore. Kind of like having a Rolls Royce, with no tires on it. Beautiful, but you
need the complete package, to enjoy it.
It's not difficult to keep using the Zenith while you can. A store that sells TV's will
be able to help, and your dish provider, can give you any other info you need.