My grandmother used to feed brewer’s yeast tablets to her dogs religiously. They took them like treats & just chomped them up–she had a chihuahua, a Lab mix & a Doberman Pinscher. I tried it with my Sheltie & she loved them, too. I found the bottles in pet supply places–regular pet stores (like in the malls) are really expensive & don’t always carry these types of products.
You can probably check your yellow pages for pet supply warehouses, or look at online pet stores–By the way, 1-800-Pet-Meds tends to be more expensive than some other places I’ve found online, but if you call them & give them the website & pricing information from the other site, they’re usually pretty good about matching the prices–plus, they offer free shipping on orders over a certain amount.
I’ve never really tried the powdered stuff b/c I didn’t need to explore any other options since my dog really liked the tablets themselves.