Zazzle has many categories you can choose from, unfortunately when creating products there is no easy way of searching the list of categories. I wanted to add a knitting related design and ended up choosing Hobbies > Achievement > Crafts. I've gone through all Zazzle categories and put them into this single flat list below. You can use your browsers search (ctrl + F) to search for keywords. Doing a quick search for 'knit', it turns out I should have choosen Art > Other Art Forms > Textile > Knitting & Crocheting.
As it's a long long list I've created separate pages:
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USA (English) (Espanol)
Candada (English) (Francais)
Schweiz (Deutsch) (Francais)
Belgie (Belgique) (Nederlands)
Please note I'm not affiliated with Zazzle in any way, I've created this section as I'm running several shops with them.