See p. 202.
You can add them to the boil, but you have to be pretty confident in the levels since you won't be able to remove the spice. I tend to add them at knockout and let them steep for 5 minutes, then remove. More often, I make a tea out of them using boiling water poured over spices, letting them steep for 5 minutes, then straining. Then blend that to taste post-fermentation. I never use raw spices in the secondary; I hate the taste.
Yes, finding pumpkin in cans is hard out of season. You can make your own by roasting your own pumpkins but be sure to use the right ones. Use sugar/pie pumpkins. Cut in half, scoop out guts, roast on baking sheet at 350F for an hour, let cool, scoop out flesh. Pretty much how you treat any squash. My CSA box had pumpkins in it starting in July last year. I used them in a saag recipe, but I might save them for beer if the same happens this year.