Not sure if this is what you’re referring to - We used Miss Design Berry for our upcoming wedding guestbook! It was a pretty easy process, took a few revisions to get close to looking more like me but overall, it’s a fun and cute thing we’ll have to hang in our home after wedding day.
I would check out Etsy for sure for any custom artwork. Are you thinking of a full book with the illustration on the cover, or an illustrated canvas for people to sign? You might also want to check out the Favors & Gifts section of the WeddingWire vendor directory for local artists and companies who can do this sort of work for you