Hi Judy,
The site below has some flower seeds listed below the vegetable list. I find most flowers last at least a few years. Some will last a long time. The ones that lose viability quickly seem to be woodland type flowers. Many of them need to be sown immediately and kept moist.
If you still feel unsure about a particular seed, you could always do the paper towel germination test. I know it works, I've had sunflowers germinate that way. If you google that, you will get lots of hits.
Remy

Here is a link that might be useful: Seed Longevity Chart

Thanks for the link, Remy. The link gave me a good rough idea of the viability which is all I expect since how long seeds stay good depends on diff conditions.