I got a few pallets from work one day that had big spools of wire shipped on them.
(I used to work construction.)
Anyway, I liked the grain on it & threw them in the back of my truck at the end of the day. I took them home & they were made of curly maple.
I took them apart. Not an easy task because they used ring shank nails to hold them together.
Anyway, I built a coffee table & matching end tables from them.
I drilled out the nail holes & used an oak dowel to fill the holes in for contrast. I gave them to my sister as a wedding gift.
That was 20+ years ago & she still uses them every day.
I've only seen curly maple pallets that one time.
I've seen a lot of oak, ash, and even some mahogany boards on pallets too, but I never used one for making pen blanks.
It wouldn't hurt to try.