The first place I would look for "fruitcake fruit" out of season is the
King Arthur Flour Baker's Catalog. See KA's website at:
I think they have a form you can fill out to get their catalog, and I
know that they have the 800 number you can call to get one of their very
helpful operators who can at least tell you if the item is available.
I also bake stollen, and sometimes stock up on the fruit during November
and December, but rarely get around to baking it out-of-season. I have
shared the recipe I use. Could you share yours? :)
Keep baking bread!