Here is a list of smallbore clubs in Devon. Most either have an air rifle section or you could shoot Light Sport Rifle with your rifle.

But it looks like the closest to Plymouth only shoot prone. Yealmpton rifle club isn't too far and they seem a really good club, I've met some of the members.

There is also an East Devon HFT club, but my emails and text to the secretary sadly fell on deaf ears, so guess they don't want new members