Depends on where you are at in Dallas.
Grabagun.com has a store in Coppell but it can be difficult to find. However, they have had different bulk packs and while the price isn't great it's still within reasonable market value so you shouldn't get hosed. They've had CCI of various types and Remington Golden Bullets in quantities of 500. They sell out but not quickly.
Other than that, hit Academy, especially on Mondays but they get shipments throughout the week. I've had the best luck with Mondays though. It's hit or miss but they have .22 all the time and even if they don't have the bulk packs you can still easily pick up a 100 rounds. Every little bit helps.
Wal-Mart has been inconsistent as hell and I haven't seen any bulk packs in North Dallas for months. If they're getting them, they are selling out fast. You can buy 3 boxes at a time though so it's easy to walk out with 150 rounds when they have it. Bass Pro Shop in Grapevine has been nearly worthless to me for ammo.
"For every problem there is always a solution that is simple, obvious, and wrong." - Mark Twain