No canonical list

There is a very obscure list, but it was printed long after the concept of forks for plane shift first originated, so for a long time there was no list. And that list was published in Dragon magazine and never again referenced, making it largely unknown; the overwhelming majority of tables will be unaware of it. In such a case, you’d have to ask your DM if it is relevant to you. On some level, there is supposed to be a specific metal for each, but what exactly is the DM’s call unless he uses that obscure Dragon article.

For reference, I’ve checked the Manual of the Planes, the Planar Handbook, and searched online for any kind of list, official or otherwise. I could not find any, nor have I ever heard of one. I’ve also checked with a friend who knows a lot about Planescape, and he stated quite definitively that no such list exists.

A comment about rationale

The rules regarding the foci get... a little wonky, to be honest. I’ll get into details below. But I think a reasonable interpretation can be found which fits in neatly with the fact that no such list exists.

It seems to me that the forks for the major planes are “negligible,” that is, found in any spell component pouch (or obviated by the Eschew Materials feat), but it is possible for obscurer planes to require forks not typically found in the pouch. So basically, there is no point to any list, because if the plane is a big enough deal to show up in the books, it’s a big enough deal to just be in the pouch so you don’t need to worry about it. If it actually needs something special, by definition it’s something small and unique to a particular campaign, so the book can’t describe it.

What the rules actually say

As I said, the rules get wonky. Here is what we have:

Rules as written

RAW, the foci for plane shift do not have a listed cost: thus they are considered negligible and covered by a spell component pouch or the Eschew Materials feat.

Note that this is despite the fact that the class spell lists have ^F (my thanks to @insomniac for pointing this out), as in

Plane Shift ^F: As many as eight subjects travel to another plane.

and the rules for spell lists state that

An [...] ^F appearing at the end of a spell’s name in the spell lists denotes a spell with a [...] focus component [...] that is not normally included in a spell component pouch.

The class spell lists are secondary sources for spells; they are supposed to indicate, in brief, information already included in the full spell description. Since the primary source for plane shift, that is, the full spell description, does not indicate that the focus component is non-negligible, it isn’t.

Intent?

What was intended is debatable; either they intended the forks to be non-negligible, and forgot to indicate this in plane shift’s full description, or they intended the forks to be negligible, and forgot that the ^F is only for non-negligible foci (or they changed their mind at some point and forgot to update one or the other).

My interpretation, based on the rules

Or, and I actually think this is the most likely case, plane shift’s focus is sometimes negligible, sometimes not, and the spell list short description is too brief to get into that, so the ^F is used to indicate that the spell can require a non-negligible focus. Note that miracle, for example, appears in the cleric spell list as

Miracle ^X: Requests a deity’s intercession.

even though only some uses (“powerful requests”) of miracle cost XP, while others (the spell-mimicking options) do not.

I think this is what was meant because plane shift itself has a caveat that certain planes may not have easily-available foci. So I think that, generally speaking, a well-stocked spell component pouch should include all major planes, but, for instance, the personal demiplane of a recluse wizard, probably not so much. A DM may choose to make this more or less of an issue, but this is always a matter of plot and not of balance.

1. Yes -- banishment says it is "a more powerful version of dismissal", and it doesn't override the 20% chance, so that is in fact how it works.

2. Given that your question is tagged "pathfinder", by the Rules As Written there is no way that the PCs could wind up in Maztica or Dark Sun or Greyhawk (as these are all D&D settings).

A very literal-minded DM might argue that, since no destination within the Material Plane is specified, the PCs arrive at an entirely randomly chosen location, which is overwhelmingly likely to mean they show up in airless deep space, far from any sun. Let's hope they have a silent greater teleport spell ready!

A less literal-minded DM might treat the dismissal effect as though the PCs had cast plane shift -- they'd appear "5 to 500 miles (5d%)" from the place they left the Material Plane.

The Pathfinder Wiki has some words about the Pathfinder settings that officially exist on the Prime Material Plane. If you're determined that the player characters arrive on the surface of a human-livable planet, but you'd prefer that it be a randomly selected planet, your choices include Golarion, Earth, Androffa, Kasath, and, er, Carcosa.

Of course, this is your cosmology; if you'd like to rule that multiple D&D settings exist in your version of Pathfinder's Material Plane, that is your prerogative.