Where can I get something like a box for Tibetan Buddhist prayers?
i do not believe there is any such box used, doesn’t mean there isn’t, but that is because the point of the jewelry was to focus the mind on one’s prayerful thoughts or secret wishes and being worn close to you was probably believed to help that. If you want a special box to use, and don’t mind it not having direct religious connections why not look for a traditional tibetan/buddhist made carved boxes. Even though it isn’t a religious item (i do know that prayer boxes are usually these days used for Sentiment rather than religion but i don’t know what your motives are) it could still be incorporated for your use and be special to you. If you are in need of something religion specific then sorry, maybe try different shaped prayer box jewelry some wont crush or bend the paper so badly http://www.prayerboxes.
