You can grow your own and many people do. In fact I would guess that most people grow them or get them from acquaintances who do.

But I would very much recommend that anyone who tries this is very well informed on the subject at least. It is a process which requires care, high degree of hygiene and experience so the product doesn't get contaminated.

At best one would not only inform themselves rigorously but also consult an experienced grower during and after the process.

Do you have a good reference to going about it?

I found some consistent sources but I would still doubly make sure if there are any established forums or papers to look into.

shroomery.org is the ultimate source of psilocybe information.

PF Tek - is an easy method to grow any quantity of mushrooms.

Cleanliness in growing mushrooms is on par with cleanliness for brewing beer. You are making a nutrient rich environment for your fungus. Best not have it contaminated with an organism that is antagonistic to your goal.