Skoob, I ran my TC3 with a diff ball missing for the last year. You'll be ok. There are even guys so obsessed with making their cars as light as possible, that they're taking out half the balls out of each diff.
But, if you are going to get more, I'd just get the standard ones. No they don't last as long as carbide balls, but neither do the diff rings. So either way you go, you're gonna have to rebuild the diffs eventually. Oh, stay away from a front one-way. They are a noobs worst enemy!!!