Where to find earthworm castings ?

[magnosis]

I've been reading a bunch of making your own soil, fertilizing substrates and whatnot.

Seems like a very good way of fertilizing Flourite is to mix it 50/50 with earthworm castings (i.e poo).  It's not mystery, worm castings is one of the best fertilizers you can ever add to your lawn, garden, house plants, etc. and has been used by many plant aquarists as well with great success.

The only problem is, I don't know where to get it ! That is, in enough quantity for a 59g tank.

Any idea where to buy this stuff locally ?

[sas]

My first thought would be a garden center and if they don't carry them, maybe
they can order them in?

Also possibly a feed store, as in agriculture.