One way is to send them to Kathy Van Veen. She roots rhododendron cuttings for about a $1. Kathy has many happy customers. It is jokingly said that Kathy could root a pencil.

Here is a link that might be useful: Van Veen Custom Rhododendron Propagation

Thanks for the link rhodyman but as I live in England it would not be practical to send them to Kathy.
I have had reasonable success growing other varieties from cuttings but no success with souliei or wardii. I suppose I'll have to consider a Misting system but I was hoping to avoid that because they're so expensive. Cheers.

I see your point. We can't get any live material shipped here. Species are usually propagated from seed. R. souliei and wardii are in the Campylocarpa section and are hard to root. I haven't done much propagation, but looking at my books I find these notes:

R. souliei needs perfect drainage and protection for its early young growth. It is very sensitive to fertilizers and horticultural sprays. It grows best in cool climates with low rainfall such as eastern England and Scotland.
R. wardii has similar requirements. [Peter & Ken Cox]

R. souliei and wardii are in the Campylocarpa section and are hard to root. He says "Campylocarpa are difficult [to root] and are better either grafted or from seed. Some can be rooted and grown away successfully if taken in late February and are often more successful if the indumentum on the stems is rubbed off." [Peter A. Cox]

Thanks again for that info' rhodyman. I couldn't find much about these two species in the Peter Cox books that I have.
The info' you've posted accounts for the difficulties I've experienced trying to grow them from cuttings and why I've lost a few that I've grown from seed. Many thanks for your help.

The second reference was "The Cultivation of Rhododendrons" by Peter Cox

The first one was "The Encyclopedia of Rhododendron Species" by Peter & Ken Cox