They're 20 a piece here, not too hard to buy multiple for 10-15 though.
http://www.shroomery.org/forums/showflat.php/Cat/0/Number/9039740/an/0/page/0 The Shroomery > Mycotopia.
I would not recommend freezing them. Psilocybin will not break down below 160, nor will Psilocin. However, there are many many other compounds...
I would skip on that and get some karo syrup or some honey for liquid cultures.
This is referred to as registering, register, etc. It's done to make sure your in a vein.
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