Looking for a good custom stationery supplier?

Not strictly tech-related, but people here have copious side projects so I figured I'd ask just in case.

I had an idea for a small over-the-holidays business with customers ordering a type of joke letter online (along the lines of a diploma or other fancy institutional-looking document) for their friends, but the important bit is it gets printed on thick, high-quality stationary and put in high-quality envelopes.

I could build a nice website to take potential orders, but I would want to be able to forward orders to a third-party supplier and have them create and ship the product after I give them a template, but I'm really not sure where to find something like that, or even whether it exists, as I've never done anything like this before.

Any suggestions?