As Dennis has said, you can't go wrong with Deceivers or Clouser Deep Minnows. LM bass are not usually too picky about the fly pattern, so there are hundreds of streamer patterns that will imitate shad.
In addition to those two, I like Murdich Minnows & Goldies, and there are the many Enrico Puglusi (EP) style flies available on most sites that sell flies. Most of Bob Popovics flies will work as Shad imitations!
There's also "bucktail deceivers" & "flat wing" streamers used in the salt.
The basic shad is white & some flash on it's sides. Some will have shades of gray, olives, & purples on their backs. Again, not sure that matters a whole lot with bass, as all of these colors will catch them.
A Google image search for these fly styles will provide many images that you can compare & select what you like.
As far as places to buy flies, flyfishusa.com, which I believe is a site sponsor is one source, Fishwest, another sponsor, and Orvis is another. I'm not a big Orvis fan, but have purchased their flies when they have sales (& I can get them cheap) and the quality has been very good. Millers Fly Shop in TX is another source, and there's a few Ebay sellers (individual tiers) that I can recommend. (Send me a PM)
I tie most of my own flies, but have over the years bought from other sources when I didn't have time to tie. IMO, you'll often get what you pay for with fly quality, some "cheap" is not always a good value. Cheap flies that fall apart quickly don't give you your money's worth. Good flies don't have to be expensive, but you should get used to paying a little more if you want good flies!