Didn't want to leave you unanswered but not much help to offer. We are ooop north and I don't know of any maths enrichment courses. At his primary school, DS gets two sessions of one-to-one maths per week.
The Edinburgh Int Science Festival is fab. Runs in the Easter hols with a programme for kids.
We've been told recently that DS (y3) is G&T in Maths and ICT. Our LA have recently stopped enrichment courses for G&T but DS' teacher told us, if we see any enrichment courses to let DS go on them. The trouble is, there aren't any locally!
I know school aren't obliged to do anything for him but wondered what other schools do and what else there is available in your area