Smallish roller cam for DD 318LA

The short answer to your question is look at the cam companies web sites.
Start with Crane, Lunati & Comp Cams. Call them and tell them what you have and what you have seen in there catalog.they will set you up.

There are small roller cams for basic improvements/upgrading your engine.
I was eye balling a 214/222 roller cam last night as a matter of fact for my 360 Magnum.
You just need to remember that ANY cam you look at can be made at the factory to fit your engine, Magnum or not.