Federal Tac I got from Ammoman, and Rottweil Brennekes I Googled around for and found without any trouble on line. Don't remember where
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Easiest way might even be from Cabela's, where I bought some low recoil Federal TruBall. Or standard velocity, if you like. They had a good selection and they'll mail it to you or you can pick it up at your local store.
I'd check with Midway USA, also.
Streichers is another possible source, and so is Cheaper than Dirt.