For graphic designs I tend to find the best designer on Upwork & Freelancer,

But If it's just for 1 journal, I'd recommend checking hatchwise.com & 99designs.com - You can start a contest there (hatchwise is much cheaper) and have tons of designer posting different ideas.

Last time I received 150+ logo design idea for a new brand.

I would do the same for a journal or book cover, the investment will be worth it.

Good luck with your project!