You can check out Pinterest. They post a lot of super pretty invites! Don't think they sell... so it's prob more for reference haha

Maybe you can ask if any local company can do what you like... i received an invite from my friend before and it was also quite unique, you can keep folding and folding and folding the card to read a story of the couple... then it ends up with the rsvp details. It's kind of like a never-ending invite. I saw the logo there was this company called stirring hearts. looks pretty decent. I think more friends are also going into postcard formats... light and fun, like those train ticket invite i also received b4.
Though you can be as unique as you want, i think sometimes the overall theme has to fit in nicely, e.g. from invites to reception decor to floral themes and hotel look and feel. Else it will end up looking like bits and pieces here and there and there is no concerted theme.