Pete,
I haven't seen 3/8" sets, but you might be able to use a 3/8" bullnose for your bead and match it with a 3/8" cove bit. I know that the WoodWorkers' Supply of New Mexico has the bullnose I can't recall seeing the cove bit. Check some of the router bit sites advertized in Fine Wood Working or other wood mags. If they don't have it they often do custom work. Another approach, assuming your not ready to drop $600 on a shaper, is a shaper head for you saw. A head is basically a heavy wheel that replaces the blade in a table or radial arm saw. It holds interchangible knives and shouldn't run you anymore than custom router bits. You can get a wide variety of knives for these heads or grind your own from blanks. If your doing any quanity of milling the shaper head is the way to go. A router and its bits will only take so much continous use. Of course the best and most expensive way to go is the shaper. Cutters for shapers that will do what you want are pretty common.

So what're you building that requires 3/8" strips?