Where can I buy design napkins?

Grocery stores, drug stores, party stores, Walmart, Kmart, Target, etc.

Walmart now has several patterns of square and rectangle napkins. They will be in the Party Dept. If you are lucky enough to have a store like Paper Wearhouse, you will find many more. Even Dollar Tree has some beautiful square napkins. A package should be about $4. You might consider some bottles with cartoon and movie designs. That would open up your market to sell these. Best wishes ☺️

I would check Amazon. They never fail me :)

I have purchased some cute napkins from Dollar Tree but not every Dollar Tree carries them. Patterns are flowers, themed coffee and shoe decor. I'm now obsessed and have a few tHemmed and designer look.

I what to ask you for how much I could sell the decoration bottles

I would sell them for $10 each, or 3 for $25. If you raise the price later, it’s because you have greater skills as you become more experienced. If you sell for $5 each, you are discrediting your time and it’s harder to come up from that. Shipping should be extra, but have a set price, according to your packing materials, postage, and labor. Very best wishes ☺️