The process I followed was,
1. Unpack chip.
2. Stare at cartridge, saying, 'now, where is something that looks like like that?'
3. Find old chip
4. Gently cut away blob of adhesive holding it in position - looked like latex glue
5. Slide old one out, slide one in. Apply blob of adhesive, wait to dry, install.
Printer worked.
Will it always work? No of course not. Sod's law always applies. But since the chips are a few quid it's always worth a try. HP laser OEM toners for my machine cost over a hundred GBP; even the non-OEM are thirty quid or so. So in my case the experiment was worthwhile.
Sourcing the things. Well, to give you an idea of what's out there, have a look at this ebay shop:
Cartridges-and-chips items - Get great deals on items on eBay Stores!
I'm sure you will find alternative suppliers by googing them.