Fairly common winter flowering clematis in my part of the world. I've seen it growing wild in Cyprus. Not sure it could take very low temps. - 10 c seems to be about the limit. Probably worth a try in PNW

When googling it many of the3 sites just talking about them were UK. I'll keep looking.

Oh you think that's hard? Try finding the winter blooming hybrid 'Advent Bells' - bred in the UK over 20 years ago, and still not available in the US.

Neither parent is anything but borderline hardy here, but I am sure the hybrid vigor would help give it an edge on survival. There are plenty of rhododendron hybrids where I know either parent would be either impossible to grow in my garden, or much harder to grow, than their outbred offspring.

I'm far from a Clematis expert, but if you take a cursory look at cultivars and when and where they were bred, it seems like there was a peak period from the 1970s to perhaps early 1990s when European cultivars were being frequently imported to the US, but that seems to have slowed to a trickle now. (This applies more broadly to various ornamental plant varities, of course.) 'Advent Bells' appears to be extremely popular in the UK by now, so it's not like this is something obscure that wouldn't be on the radar of collectors here.

If it's any consolation I have had Wisley Cream for years. It's rampant and reaches high into the branches of an apple tree. This winter it had 1 flower. An improvement on last year. I keep it as it screens next door.

Maybe you need to try to find an 'Advent Bells' 🤣

Seriously though, it obviously isn't too cold where you are, so I wonder why it isn't blooming well. Maybe it needs more sun?

For reference:

https://www.clematisinternational.com/page218.html