Lucas Starks
You can see a lot of those here:

Emit Flesti
I do not know of any retailer in the UK that sells these. I'm not sure if this is because they look like realistic firearms and as such may be covered by the VCRA. (if they are covered then it would not be worth importing them) Is there specific reason as to why you would want one of these? as there are far better air rifles available for a similar amount of money.