tek light issues (ballast?)

[Skimmer Juice]

Currently running a 36' 6 bulb tek light t5ho fixture , yesterday my my light just turned off. The switch still turns green when on just no bulb's turn on.
The swtch that control's the 4 middle bulb's is the one that does not work, the other swicth controling the 2 bulbs works fine.
Thinking its a ballast problem , does anyone have expierence with this problem?
What did you replace the parts with , anybody know if you can find a ballast locally (calgary) or will I need to order the parts? And what ballast should i go with ? Thanks for any help/info