Dowflake
You can order it online, its really dirt cheap but the shipping will kill your wallet, that said, I bought a 100 lbs. and it was still cheaper with the shipping than a 5 gal batch of B-IONIC 2 part would cost me.
I know you don't need that much so you could look into hooking up with a couple others and sharing the cost.
And finally, you can use PelaDow, it's easier to find than DowFlake. You just reduce the amount to 400 gm. per gallon. Or you can use something like Kent's TurboCalcium, but at that point your into not saving much $$$.
And the thing is that the measurements don't need to be that accurate either, after all, your dosing and measuring .. if the concentration varies or your usage increases/decreases you just variy the amount you add.
I use Kangaroo feeding pumps to dose with, very accurate and the system is very stable day to day .. I just tweak it up as demand increases.
Regards
Noel
P.S. Iris sez howdy!!