You don't have to buy a new bladder, even if it's got a
1 metre rip!All bladders can be fixed. It depends on what you have to fix it with and types of glues, etc.
But it's not rocket science. I've experimented with glues and patches and found the KiteFIX kits are well worth the initial investment (
www.kitepower.com.au/collections/kitesurfing/Parts-&-Repair). They repair just about everything that you cannot do without a sewing machine.
However, in your case a 10cm cut is not bad.
If you really want to replace it, just find any bladder for a similar 8mt kite (or even a 9mt) as long as it's close to the length of your own bladder's length and max width in the middle.
It does not have to be the exact same bladder, contrary to what many shops and people say. The ends are folded back anyway! There is a guy on ebay that sells bladders for $50 tops. Or buy a 2nd hand kite that's been damaged and keep it for spares. Buying new bladders when all it takes is a couple of proper patches, is wasting your money.
Unless it's a valve repair. They are mostly not worth repairing and you can buy replacement valves cheap.
Google bladder repairs, buy a kit and do it yourself.
Most kite repairs can be done by yourself.