if things go my way, I'll be looking at large quantities

I agree with Billy that you might want to look into finding a local seamstress that can help you out at least at first.   You can always look into moving to a larger manufacture in the future but that could cost thousands of dollars to get going. Big investment up front as a rule.

If you know what you want (a pattern would be helpful), run an ad on craigslist.  Note that you are looking to find someone to sew in bulk, and you are willing to pay ___ per item.    I have done this for some other stuff and was swamped with replies.  One of my criteria was to ask each person to sew one of the items for me and return it (I cut it out, mailed it with directions and paid return postage).  That's a quick way to sort out who can and cannot sew well, and the amount of time it takes them to complete an item once they receive it.

If you are going to be near Vegas in August, you might want to check out MAGIC. http://www.magiconline.com/
You want to go to the sourcing pavillion at the convention center. You can walk around and talk to all of the manufacturers there, and get an idea of the costs, etc. If that's not an option, you can always try to find a sourcing book from last year's convention. They give out a huge phonebook/resource book at all of the information desks on the floor breaking them down by country, etc.

Good luck!

Have you thought about thought about....Build-A-Bear.  They have nice size clothing for smaller size puppets...plus you can buy there blank shirts in white and you can print out designs to iron on them if you want to personalize the shirts more...ask them if they will sell them in bulk to you??

StiqPuppets