Hi there, I’m from the U.K too, you can buy silkworms or silkworm eggs /starter kits easily from thesilkwormstore.co.uk or eBay or silkworm Safari, my veiled absolutely loves them.
I buy eggs and raise them, i don’t find them the easiest to raise but their nutritional value is worth the effort, I also have a bin of Dubia roaches, they are easy to keep, don’t smell and pretty cheap to set up, you’ll find he can’t manage larger roaches but you can always sell oversized or excess on eBay and buy something else with the proceeds,
I raised Indian stick insects, a bit of work collecting bramble but a possible, eggs and nymphs found easily on eBay,
Onlinereptileshop.co.uk sell curly wing flies if your Chameleon is small, I also buy blue or green bottle fly casters from wormsdirect for something different but it increases the risk of you having blue bottles flying around your house, I personally don’t feed crickets but locusts are a real favourite.
As a rare treat I feed pachnoda grubs, and am setting up a colony as they are fairly quick to breed and produce larvae, probably not worth you doing for one Chameleon though but they are easy to buy as larvae, but you’ll have to wait until he’s full grown as they are quite big, I snip the mandibles out before feeding by the way, they nip and they are only as a rare treat.
Calciworms are great if you buy a box and leave them to pupate and emerge as flies, they are slow flying and easy for the Cham to catch. I also buy waxworms and let them turn into moths, my chams love them!
Remember to gutload what insect types you can and keep them nice and clean, clean bins, cages, remove old food etc. There’s lots of info in the caresheets here about good plants for gutloading etc.
Hope this helps a little.
Good luck with your quest.
