Highest critical range for archers?

[Twoswords]

What is the highest critical range that an archer is able to achieve?

I know Bracers of Falcon's Aim takes it to 19-20
I know Keen takes it to 19-20.
I know Improved critical doubles the threat range, again taking it to 19-20.

What I do not know is if there is a way to increase critical chance even further? I am looking for options both to cause a critical hit as well as confirming the hit.

[Daenar]

Archery is generally considered a powerful option. However, expanding the crit range of a bow past 19-20is as far as i know not an option. Sorry.

[Kazaan]

The best you could probably do is a lvl 20 Fighter with Aspect of the Falcon cast on yourself (would require either Gestalt or a Wand and UMD check). Aspect takes your bow to 19-20/x3 and Fighter's capstone ups it again to x4 and lets you auto-confirm.

[cnetarian]

Crossbow can bring it to 17-20 (19-20 base), although the character will need rapid reload/crossbow mastery to make it work, by sacrificing the X3 damage for an x2.

confirming there are a few ways to increase that - the critical focus feat, the mythic critical master ability, kensai critical perfection ability, the unerring weapon spell and so on (including the fighter capstone previously mentioned).