Option 1.
Have them fight a baddie from said plane and the baddie casts a spell and (you fail your SR check) that forces the party into the new plane.
Option 2.
You find a portal and want to destroy it (because it is magic) and in the process of destorying it, the magic explodes and send you to plane X.
But I have a few questions that I just can not get out of my head.
How can you be a Fighter 3/Forsaker 7? Isn't that a little low to qualifiy? (I guess that the DM made an exception for you.)
How can a forsaker be a member of a party of spell casters and/or magic item using characters? (I don't think they can, I would expect that your DM had to make an exception.)
If I am right about those two things, then I think the way to get your forsaker to another plane is pretty clear.
g!