You used to be able to buy individual sears by Laylax or PDI waaaaaaaaaaaaaaaaaay back in the day (we're talking like 2008 time, when I was first looking at building a VSR), but over the years these have been phased out in favour of complete trigger boxes; even back in 2008, the Laylax Zero triggers and PDI V triggers were starting to muscle in on the individual sears market as the best option for upgrades.
I found a set of Action Army 90 degree sears here (
https://www.combatsouth.co.uk/action-army-reinforced-sear-set-for-vsr/), but at £70 you're better off getting an S-trigger or Namech Flux trigger, as I don't know how tough the Action Army sears are (I'm guessing they're the stock sears in the AAC T10), and the full trigger units are rated for way more power than we have access to in the UK.
That said, with a fairly efficient build, I got up to 2.2J with an m120 in my VSR, so if as Skara says the Action Army sears are rated for m120 springs, you may get enough power, but if not... that'll be £70 of sears just waiting to snap. The S-trigger is rated up to m190 springs and the Namech is apparently rated up to m220 springs, which are far too strong for UK limits, so you won't have to worry about them giving up under normal usage; even with a horrible short barreled build slinging .2s for maximum inefficiency you're probably going to be well over 2.3J with those springs.