There are a few options:
1) Pulsing in a food processor. This will likely take a long time, depending on the volume of grains, and may give you too fine of a grind which will be a problem if you are mashing in a mash tun and are going to sparge. From what I understand, some BIABrewers actually prefer a finer grind because they don't sparge and the increased surface area gives more access for the enzymes to go to work on the starches.
2) Put enough of them in a Ziploc bag to get a thin layer when laid flat on the counter and roll over them with a heavy rolling pin until you get to a decent crush. This, too, will take a while depending on grain volume, and may provide a more coarse crush than you are looking for, but won't be as susceptible to the the problem of stuck sparge as the previous method, or even a regular grind you'll get from your LHBS or online retailers.
If you're just steeping specialty grains, I would go the first route.
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