I use canned pumpkin for my annual pumpkin ale. Typically, I use the solid pack 100% pumpkin cans. I have in the past used the pie filling cans and it was surprisingly one of the best pumpkin ales I've made. I had a hard time finding canned pumpkin this year and it may or may not still be available.
Alternatively, you could try using sweet potatoes or yams. I did this many years ago and cannot recall if it was noticeably different in flavor from pumpkin ale.
As mentioned above, much of the character of pumpkin ale comes from the spices. Lately, I've been making a tincture with vodka and spices and using that to flavor the base ale before kegging.