SS lugs are available but there is a more limited range of tube sizes and joint angles.
There are almost the same sets now in SS as in standard steel -
if we're talking about modern lug designs.
There is less freedom with lugs than with filet brazed, but that's simply because when you use lugs you end up with pretty much the angle defined by the lug (you can bend them a bit to compensate).
There is plenty of choice in stainless dropouts and fittings. The dropouts, fork crown and all the fittings (including my 953 chainstay bridge) on the frame I built with Dave Yates are stainless. There was loads of choice out there, you just need to know where to look.
Start with Ceeway and Henry James and you'll see there are loads of designs out there.
Why not go with Lee Cooper for a frame?