i work at a pharmacy and we have a plethora of empty gelatin capsules. though i'm not the one that buys them, my guess would be they are available for purchase at a medical supply store. check your phonebook or go into a local pharmacy and ask them for the phone number of a nearby medical supply store.

if it was me making these marijuana capsules i would just put ground up marijuana into a capsule and take about 5 of them.