I have no idea what is in a Power Pack C either Douglas, but just like you, I have Internet access so replicating a Power Pack C is NOT difficult. I've done it myself numerous times. In fact, I have purchased my own version of their power packs for all my many F.T. foam airplanes and I've never had any trouble.
Rather than give you a fish, I'll teach you to fish if you aren't offended by a Biblical reference. If you plan to do any serious RC flying, you need to know how to shop for components. It's not hard at all. Do this:
Google Power Pack C or go to the Flite Test site and see what the Flite Test PP C contains. Note the motor output and weight, or Google the motor specifications and dig them up elsewhere. Then go to your favorite source and purchase a similar motor. You may have to search several RC outlets to find what you want in stock and/or at a good price. Just use ordinary Internet shopping techniques.
Claimed output seems to vary quite a bit from manufacturer to manufacturer so take what they say with a grain of salt. That's why you also want to compare motor weight because I've found it to be as good an indicator of performance as is the claimed output. Another peremater which might help is the way some sellers recommend their motors for airplanes of a certain weight; for example, "suitable for airplanes weighing 150 to 250 grams. Take that data with a grain of salt too, but every hint helps. Remember that for the typical foam board airplane, an DIY combination to replace the Flite Test Power Pack C need not be an exact match.
Pick a similar ESC, prop, and battery and you're good to go. This is NOT rocket surgery, as they say. Close is almost certainly going to be good enough. Normally you'll want to be sure your ESC has a power connection for your reciever (some don't) and pay attention to the type of connector used between the ESC and battery. Of course they much match. All batteries will have a connector and most times you can select the one you prefer. Some ESC's have connectors soldered on, some have a loose connector in the package, and some have no connectors at all. So, if necessary, buy a battery connector too.