Not for canning (I do can) but we use quite a bit of citric acid for making bath bombs. The brand is Roots Circle. No SiO2. Crystals about like sugar crystals. 30 Oz. Don't remember the price. I think we got it through Amazon, but here's a suggestion to check your local hobby store in addition to the grocery store for larger containers.
Found it on Amazon. The price isn't awful, but it doesn't look like the packaging survives Amazon's packaging and delivery system well, from the looks of the reviews, and they don't consistently do freshness seals to prevent hardening into a clump... or when they do, there're monkeys in the works that tamper with it. Also, looked up the OU Kosher certification, as I got burnt on that with the last batch I bought. At least it's half legit. The product's in the Orthodox Union database, but it's not certified Kosher for Passover, despite the label on the side. Not that I'm that overly observant with kashrut (I'm willing to go without on this, given the LemiShine), but it's nice to have multiple supervising authorities over the product quality... especially for something like this that you plan on ingesting, I'm finding. But, if you're willing to lie about one thing on the label...
The local big box hobby stores (that's all we got, we're in Green country) don't carry food grade, and of the local grocery stores, they either carry Mrs. Wages, which contains 2% SiO2 and runs nearly $10/12oz; or they carry Ball Canning's own brand, which if you're familiar with the canning space and the prices there-in with these legacy canning brands? You'd think the stuff was lovingly produced over the course of months by the hands of vestal virgins, and each 7.5oz shaker was rode into the store individually, swaddled by a cashmere blanket, on the back of a neutered Ane de berger jackass.
So, this is not a personal recommendation but how about Milliard? Appears to be GF, not have silicon dioxide, be available in bulk, and have good reviews.
I was thinking about Milliard next, but despite the reviews, I've gotten a little gun shy at this point... especially as I'm not familiar with the brand, and the rest of the Amazon store for Milliard branded stuffs is all non-edible, BBBY-style home-goods.