Trust me, you don't want to add a moisture source . . . you'll kill everything. All you use is enriched UNBLEACHED flour. That's all I've ever used, and my current culture comes from a line of cultures my father and I have been keeping for almost 10 years now.
If you just change the flour every 4 months or so, you'll be fine. I personally use a little sifter that looks like a screen cup with a wire handle (3 for $1 at the dollar store) to scoop 'em out, tap out all the flour into the culture, then I let the larvae wriggle through and drop into another container. Then, I put the beetles back into the culture to lay more eggs. If this is a new culture, it might take a month or two to really get established. If you were sent a well-established culture with lots of eggs, you should be in business.
Best of luck,
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Homer W. Faucett III, esq.
Purveyor of Trivialities and Fine Nonsense