As for availability capping at 9:
You could make a "by RAW" argument that yes that's the case. This would then by extension mean that Power and Weapon foci can never be higher than Force 6.
I can't promise that the splatbooks and other published sources don't have odd examples of availability ratings higher than that though. I wouldn't necessarily agree that saying gear can't be modified/come in ratings that would push availability past 9, but it's reasonable enough. I mean, really, once you go past that, good luck finding a contact who will have a sufficiently high connection rating to acquire it.
Edit: As for chargen, where yes technically availability doesn't matter unless the item in question is illegal: then use your GM powers to just make foci of unacceptable ratings illegal in the setting in which your campaign is set. QED!