I use X-cut punches. They come in different sizes but all make lovely tiny to teensy little envelopes - ideal for tiny seeds. Google X-Cut and have a look and see what you can find. Mine are quite old so they may even have some in the end of line type section for quite cheap?
Here's one for 9.99
http://www.craftydevilspapercraft.co...raft-punch.asp
This is a template for an envelope - unfortunately out of stock but maybe you could order? 1.99
http://www.craftsulove.co.uk/templates.htm