Get another HomeRun dual, luckily it on sale today for $51 at the egg using V.me coupon code.
We have 3 of them in a 6 tuner set up (along with Ceton InifniTV6 ETH).
You are not going to find more than 2 tuners per pakcage for ATSC, not yet. Maybe SiliconDust will finally release quad ATSC, maybe not.
Edit: You may need a drop amp to split your antenna signal, or signal amplifier and splitter. We have 2x of the older gray duals that have inputs for the individual tuners, and one of the newer single input tuners. 6 port drop amp works great with antenna input.
Multi-tuner units have internal splitters, it is not like singal is magically split between all the amps inside. You may be better off with smaller count tuners, so that you can contol signal drop with splitters/amps instead of locked down internal split.