If you're looking for seeds, why not step out and collect your own? Of course, only some of the plants will have seed ready to harvest, but that's what makes it fun. The primary rule might be to collect only as much as you need and only from well established stands.

One source I've found valuable for nursery listings is CYNDI'S CATALOG OF GARDEN CATALOGS.

However, whether self-collected or purchased, the UK plant protection people might not let whatever you obtain into the country

Here is a link that might be useful: CYNDI'S CATALOG OF GARDEN CATALOGS

Thank you - I have brought packed seeds back from the US before with no problem - it seems to be only a problem if you bring something living, with a root etc.
Pardon me but what do you mean by established 'stands' - do you mean people who sell by the roadside? It's not an expression I have heard before.

Hi Barbara...

I'm a big fan of the Reno area...be sure to check out the Black Rock desert, and Pyramid Lake. Both holy sites for Native North Americans, and isolated and wild and free. You can hear yourself think. If you want an arty thing to do whilst in the Reno area...check out Guru Lane. It's in the Black Rock, and I can't really describe it...but I'm sure it's on the net. Let's see...have a buffet dinner in a casino in Reno. Check out the Sierras! Go to Wally's Hot Springs and have a soak! American Falls! Go look at Lake Tahoe...look at how clear it is, and realise, sadly, that it's losing 8+ feet a year of it's clarity due to run-off from nearby lawns (inorganic fertilisers)and parking lots(oil, transmission fluid, etc).

Sorry, by established stand I mean a healthy well established natural population. Less than healthy populations may need every seed they can produce just to maintain themselves.