I am having trouble finding seeds for miniature/terrarium plants, such as succulents, African Violets, and other suitable plants.
To locate seeds for miniature plants for terrariums, you need to establish a list of them with their scientific names. Then do a google search on indoor plant seeds. Some that I am aware of include 'Brazil Plants', Gesneriad Society, African Violet Society. A good source to locate seeds are local plant society chapters. Many have annual seed workshops and other members will help you locate sources. For example, Liberty Bell Gesneriad Society is having a seed workshop next Tuesday in Philadelphia. 141 seeds have been acquired. A few of them are miniatures. Also, members share plants and seeds. It is easier to acquire plants. Many nurseries carry them, such as Primex, Bucks County Nursery, Longwood Gardens, etc. Gary Hunter Specilty Plants is a major grower of miniatures in Delaware County.