The reason you haven't been able to find bamboo seeds is because specific species flower infrequently (at intervals of 20-150 years). Therefore, if you want a specific bamboo, about the only way to get it is to get a division of another plant. There are seeds for a few bamboo available occasionally because several of the 1200 species of bamboo are in flower at any given time. However, you encounter the following problems with seeds:
-they lose viability quickly, so you have to know it's fresh
-germination is hard with some species
-successful germination will result in plants that are small for a number of years
-many species may not grow in your climate Zone
-it is illegal to import seeds from outside the U.S. without a permit and lengthy quarantine

So, I suggest you find someone willing to share, or buy some that is hardy in your Zone from a reputable, local or online bamboo nursery.