In ours, the coolant is referred to as "PG25" (distilled water with 25% propylene glycol, plus corrosion inhibitors and other additives). It's widely available, and pre-mixed so it just gets poured straight in.
Your problem is going to be quantity. it might be cheaper per unit, but buying less than a 200 litre drum (if not a 1000 litre IBC) will prove to be a challenge.
I'd suggest a rethink, honestly.