I would like to grow Asplenium trichomane between paving stones on my patio

Asplenium grow from spores rather than seeds and are not easy to propagate, hence the price. I would suggest that you just buy one plant and hope that it will do its own thing. A number of years ago we had one just turn up in the garden and now they are all over the place. A lovely little fern.

Thank you Bulbaholic. I had read that they propagate from spores, but, not being terribly knowledgable, wasn't sure if that meant they also had seeds. I shall have to bite the bullet!

It would be fun to try from spores as well though.I have grown Drypoteris from spores and it was easy but took a very long time. If Bulba says Asplenium are more difficult so be it but as well as buying a new one I would be tempted to have a go because it is (slightly?)more likely to work than if you don't try.. Nothing venture nothing win. I can't remember where I read the instructions but I can remember what I did - if you PM me I can send you the method i used.
You 'll likely have to wait until later in the season though because they probably haven't got ripe spores yet.
Its worth reading up about fern propagation because you wouldn't believe what goes on! Quite different from seeds and it explains why ferns need damp situations for at least some of the year.

I have not tried to propagate them, S, but it is what I understand. In our garden they seem to do quite well without my 'help'!