Hi jen - maggots breath through their bums, and they breath oxygen, so best to suffocate them if you can't get hold of crovect to treat. Try thick sudocrem or vaseline over the offending patch once you have picked out what you can.
You can shear lambs in the first 6 months, that's fine - many people shear lambs to stimulate their growth. Don't leave it too late though...
Best thing to prevent flystrike is still clik, although understandably there are some sceptics on this forum. Really, best thing to prevent flystrike is good luck, and then keeping your eyes open and treat what happens!