If you buy a bait tank, make sure it contains a charcoal or zeolite filter. Those tanks at Cabelas are worthless. You can aerate all you want but it's the Ammonia from the shad pee and poo that causes all the issues. I think TCK73 is right that PK tackle carries tanks. Just make sure they have a filter.
Yep, if it's for shad, aeration, and filtration are a must. Having a current also helps a lot. I use a 17 gallon Grayline. Keeps them alive for days, if I need it to. If you're keeping them in it for more than a single day, make sure you clean the filtration, and do a partial water exchange.