I'd say that there's a lot for sale for a few reasons:

Firstly, they're good guns, so plenty have been brought into the UK.

Secondly, lots of people are Weihrauch followers.

Thirdly, they have anti-tamper that is much more fearsome than people realise. I suspect a lot of people have been shown online "power up" vidoes and have been bitterly disappointed when confronted by the AT and want to get rid.

I currently have four HW100 variants. I once had six - and I will shortly have six again.
I have one more enroute that I recently bought.
I also have a friend holding a wrecked one, that I'll collect when the weather is better.