Very few aquarium plants produce seeds, and hardly any while in a submersed form. Getting viable seeds from emersed plants is not very easy. The plants need to be pollinated, and then the seeds have to be collected. Then there is the difficulty of growing the plants from seeds (most seeds cannot be allowed to dry out before being planted). It is much easier to grow plants from stem cutting, splitting rhizomes, root division, etc. You will find aquatic plants that can grow from bulbs (lilies and aponogeton species). These are available in many lfs and on-line.