A couple of years ago I bought MgCl from Univar. I used my company name to buy it , and they hade minimum quantities.
PK Building is just around the corner from my shop, and I've bought Dowflake there, but again not for a couple of years. I found it mixed up quite dirty, and with some sediment. I wasn't really comfortable with this.
Put a lot of effort into sourcing Tetra CaCl locally. The Tetra rep, I beleive in California, was very helpfull, but their local distributor only sold by the truckload
In the end I've found it much easier, and cost effective (if you consider yor time) to just order from Bulk Reef Supply. You could try to get in on a group order (or start one) to offset the shipping cost.