[Northerner]

LEE Precision molds are usually reasonable in price. I have a .319", .375", .44" and .457" ... all LEE. It looks like there are dealers on your side of the pond too... with 4 in the UK.

https://leeprecision.com/dealer-distributor-resources.html#Europe_R

 

[Northerner]

18 balls with .330" or .360" diameter.

https://leeprecision.com/bullet-casting/buckshot-molds/