The two tires you mention above are the same. Just inconsistency in what was written. The C refers to the specific type of rim in question, a 700c rim. And, all (for all intents and purposes) 700 rims these days are 700c. You won't find a 700 tire that is not 700c without a lot of effort and special ordering. There were different versions of the 700 rim in the past, but they are obsolete and there's no chance that Redline uses them.

So buy the same tire, from the same place you bought them in the past.

Just as a nit, and many people including businesses do it. The diameter is 700c, the width of the tire isn't 28c . The width is 28mm. But most people just write 700X28c, and many refer to a 28mm tire as 28c. But that's might be what confused you.

To make it even more confusing, the 700 refers to 700mm, but that isn't the diameter of the rim itself, it is the estimated diameter of the rim+the tire. The rim diameter is actually 622mm. So, you'll actually probably see two specs printed on the tire: 700cX28 and 622X28 or some variation of that. It all means the same thing. Bottom line, again, is buy the tires you're already familiar with, they'll be fine.