As far as I know, GK uses their OEM design made by Eminence. Give
Orange County Speaker Repair a holler and they can recone and/or repair it anywhere from $55 - $65 plus shipping. You will have the speaker designed to be used in that amp/box with a new lease on life. If you replace it with an after market speaker, you may not be pleased with the end result...then you wind up paying a whole lot more to make it right.
These guys are the best in the biz and they have a quick turn around time. I've bought a lot of cabs with creased speakers (can you say cheaper purchases) and they've made them right with absolutely no problems.