Cardoon;
http://apps.rhs.org.uk/rhsplantfinder/nurseryfinder2.asp?id=76926&d1=9&so=pf&mo=N

Geranium;
http://apps.rhs.org.uk/rhsplantfinder/plantfinder2.asp?crit=geranium+and+psilostemon&Genus=Geranium

Astrantia;

http://apps.rhs.org.uk/rhsplantfinder/plantfinder2.asp?crit=astrantia+and+shaggy&Genus=Astrantia

cirsium rivulare" atoropurpureum"

Don't know!

Campanula;
http://apps.rhs.org.uk/rhsplantfinder/plantfinder2.asp?crit=campanula+and+lactiflora&Genus=Campanula

aster xfrikartii "monch

Don't know

When I say don't know I mean the RHS does not know either!

I hope that helps!...Tg

thanks TeeGee, most helpful, i will investigate .

kind regards doogiedog

Almost any garden centre would sell these plants. They are herbaceous perennials though and not 'bulbs'. Perhaps that is why you have not been able to find them.

I was thinking the same as Owdboggy - most of these are stocked by all my local GCs.

Most garden centres normally sell plants that are in flower so customers can see what they're getting (very useful if they don't know anything about plants!)
If you go to Plant Finder on the RHS website, you can find nurseries selling the plants you are looking for - some may be local so you can visit them; others may provide plants by mail order.
If you are unsure how reputable a nursery is, you can ask another question here to see if they are recommended