I hosted a Baby Shower Tea with another gal not too long ago and we found the perfect invitations through ebay for super cheap. The invites were hand made with our information included. We did the tea cup invitations, which can be done with different paterns depending on boy, girl, or unknown color schemes. It was a fabulous way to invite people and they couldn't stop raving about the invitations and shower. Here is a direct link to the vendor that sold them to us through ebay: www.apartywish.com. The invites were super cheap for what we received too! Some things we did to make a very "baby" themed tea was made diaper cakes as centerpieces incorporating some of the small items for which she had registered. We were able to buy many of the accents and supplies at the 99 Cent store and Dollar Tree. We floated some rubber duckies in the water/punch bowl. Just some ideas if you decide to go that route.
Another place to look for invitations is at the following:
The Art of Paper
19654 Ventura Blvd
Tarzana, CA 91356
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They have an unbelievably large collection of fabulous invitations and stationary. You can either pay them to print the invitations for you, or in many cases, you can print them on your home printer.
Best of luck in finding the perfect invitations!