sleeping bag zip

i am in the armed forces and have a few softie sleeping bags off a couple of mates all of which the zips are broken we were wondering if you might be able to repair or replace them as they are a good bit of kit which we are reluctant to chuck out for what seem's to be some kind of defect

Zippers can usually be repaired or replaced. Find a gear shop in your area and ask them who does their repairs. Some stores will have repair departments, but most probably send out this kind of work to a specialty repair shop. Also, look online. I know of several places in the US that do this kind of work, but it sounds from your post that you might be in the UK.

I'm sure you could take it to your local tailor shop. They can rip out the old zip and sew a new zip like a professional. They might even have catalog or supply shop to buy the long, heavy duty zipper from.