What do they look like?
Try vacuuming up everything and usic Boric acid dust or similar crawling creature powder on the floor. If it is the beetles I see occasionally, they are confused flour beetles (see Google image search), and they don't have chewing mouthparts that are very effective for whole grain, unless it is roasted at least 10 L. Munich 20 L and C80+ seem to be favorites. Malt dust is their favorite and you can see random trails in the dust. Imagine their delight if they eat malt dust (and not very much) to find grain dust all over a malt room. Dust collection or control on the mill or malt transfer system helps immensely. Removing them from a mill can just be done by persistent vacuuming...and getting rid of the vacuum bag which they will just fester in and eventually crawl out of.
I would guess gestation is about 3 weeks, maybe less in warm weather, so anything sitting around that long is suspect. All open bags should be in plastic tubs or such, where there is some containment, or at least you can tell where they are coming from. I tried putting dry ice in the malt tubs to suffocate them, ut it was not as successful as I had hoped.
Basically, starve them out.