The Charge Blades can be gotten different ways. One is a guaranteed reward for doing a challenge. The others can be gotten if you have the rep points and scrip.
Here's a key to actually getting the challenge done-I won't say that if I can do it anyone can because that's not fair to anyone. I will say that it is possible.
First off, of course do take into consideration some of the strategies others have stated but as far as weapons go that you will use-consider those that you work best with and know the best. And those that you have mastered with good bonuses, and weapon types that are maybe at 20. Maximize your potential. Don't get too focused on weapons others found success with-and one loadout won't necessarily work for all arena types. Also consider that the weapon you use can add to any lag you are experiencing. I avoided BMGs and explosive weapons for this reason. Lag will mean fewer minor foes for keeping up your multiplier.
Perks-try to avoid reloads. What got me gold for the last arena the first time was Dual Cankers (I've also doneso with a SAW and a Canker, an SMG and a Canker and others use Invaders and even someone that I helped recently got it with an Incubator)-one with grenade refresh and one with EGO refresh and I used the Infector grenade as well as Preparedness perk so my stowed weapon was always slowly reloading. It's then the case of the EGO power (I use Overcharge) and making sure that whatever perks and EGO power you use are maxed. I used some perks to bump overcharge or EGO power, some damage enhancers, and one protection perk. A good shield based upon your strategy helps too. It might be a respark for the quick recharge or an ironclad that maybe gives you time to seek cover. The higher the EGO sometimes the better for shields as well.
Until you have gotten silver or gold if that's what you want-don't obsess over the gold skitterling. If you have a good multiplier going and he's there and easy to kill, do so but don't chase him. You will only force your multiplier to keep dropping. It's perfectly possible to get gold without him, and if you want to get him, you can come back and do so at another time. He's a distraction.
Keep killing the minor guys-I got gold by mostly killing them and just by keeping that multiplier up.
And all you have to do in each arena is look at the kill value you have to reach and get to 2000 less than that and survive the arena. If the Bronze value is 4000, you only have to hit 2000 and stay alive-you get a survival bonus of 2000. So for the last arena, you need to get to 8000 for gold and survive.
Lag. If you're in an arena and you find it's kind of empty, not a lot of minor guys or enough foes to keep the multiplier up, just do your best to get to bronze-you'll get rep points for it. Then, either try a different phase-log out and back in again or wait for a less busy time for the servers or your area even. It may or may not help but it's worth a try.
Again, I'm not saying everyone will find this easy. It wasn't easy for me, and it had some killer lag at times-sometimes, there were very few foes and sometimes they were flying in the air or zoomed across the arena and then were suddenly behind me. But there have been times I've had very good run throughs with a lot to do. I got to 1000 rep by doing contracts and repeating the arenas and got silver quickly enough even with some nasty lag.
It's a challenge and can be very hard a lot of the time.

