An old latch type lock (Wealdstone HA3)

Hi I need to get new latch return spring to fix one of my door locks so I am wondering if anybody has an old one kicking about (or attached to an old door they are getting rid of) so that I can take the spring out of yours to put into mine. Even better would be someone who has the spring which is an asymmetric one avoiding me cannibalising another lock. This would save me having to replace the whole thing, get keys cut to distribute to my grown up kids etc. I can collect quite easily anywhere in the Oyster zone as I use public transport.