I think you should be able to get a spare spring for it – ask around [try scrappies too] its not the worst part of the gearbox to fit [or the nicest]
You can drive with a knackered gearbox for ages but only if you are a good gearchanger [dont rely on the springs too much]. I had a car with a screwed gearbox for 2 years and I got around in it no problem as I always push/pull the gears using the base of the stick [box had worn selectors, a bust spring and a decorative gearstick knob – it came off if you tried to use it] In all fairness I have to point out that no one else ever wanted to drive that car twice :groucho: but it passed its mots and I needed transport 😉
I would recommend getting it fixed if at all possible, a broken spring does not a shagged gearbos make but using one with a wrecked spring could damage it pretty seriously if you grind it constantly, crunch gears, etc etc
fixing it may be annoying but is far less hassle than replacing the whole gearbox later on :groucho: