I have played a few games with zerg and have had some difficulty running the 'ground pounder' route.

When I say ground pounder, I mean defilers and ultralisks. They have a lot of difficulty when in facing numerous flyers.

I suppose that I could invest in zome scourge to counter this, but I find that I am strapped for gas with defilers and their technologies... plus using hydralisks to counter air. Hydralisk cards are few and far between.

It seems like I am forced to go the route of air with the zerg to be really effective.. there is no real viable A.A ground units where both the Protoss and the Terrans have several options (protoss with archons and dragoon upgrades, terrans with goliaths and the fact that marines can hit air which is just super powerful).

I think when opponent goes mass air the best option is air too.. but if you dont want you can do hit and run tactics on lonely air units like attack with defiler and use burrow+plague for example and have as many zerglings as possible to occupy enemy resource areas

Another option is the anti-air module. If your ultralisks and defilers are stuck on the defense, just pull them into your base. My friend has used this on me numerous times, and it has always made me frustrated. You can also have ultralisks and defilers guarded with hydralisks. They aren't all that bad against air units.

There are methinks two hydralisk cards that boast a 7 vs. Air attack, which isn't half bad. On the defense, it may not be too good, on the offense, with supporting hydras and the +1 attack card, more than enough.

Scourges are obscenely good vs Air - while in the computer game attacking a battlecruiser with scourges was folly and fruitless, here, one scourge has a good chance to bring it down if the battlecruiser doesn't use yamato gun. And, you can stick an improved carapace on the thing too, if I am not mistaken.

The scourge costs 1 gas. No real expense for taking down any other flyer.

Also, Dark Swarm makes all the flyers weep, for none of them can attack your precious ultralisk then.