I have red, pink, fuchia, and ivy geraniums. I have done cuttings and bought seeds. I don't know where to find the seeds on this plant.
The seeds of pelargoniums ("annual" windowbox, zonal, fancy leaf or ivy geraniums) can be found on old, spent flowerheads that have been allowed to remain on the plant and dry and ripen. These plants tend to be scant seeders and the seeds difficult to collect and germinate - they have a hard coating that requires scarifying or abrasion before planting and they are tiny! And a good many are hybrids, so depending on exactly which plants you are harvesting seeds from, they may not come true to the parent plant. But that doesn't necessarily mean you won't get very nice flowering plants via this method. To get exact replications of the parent plant, cuttings are best and they are extremely easy to take with pellies.