If we are talking JARs, then all the data is on the JAA site. It is a copy of FARs, so I suppose the same information is on the FAA site.
JARs give a fairly basic definition of Va, which is a design speed, assessed as basic stall speed times the square root of limiting positive g.
Vb is the design speed for application of gust criteria for certification. The definition is complex, and is in JARs in full.
Vb is higher than Va. Rough air speed is not a design speed. It is a recommended speed, chosen to give you the best chance in turbulence of not hitting either the low speed or high speed buffet boundaries. Again, JARs explain how it is chosen, but a simple explanation is that it has to be higher than the minimum calculated
Vb, and can be about half way between Vstall and Vmo/Mmo.
Although Va, calculated at max. certificated TOW, will not change, published limiting speeds for manoeuvre or for full control deflection will change with aircraft weight, as basic stall speed changes.
But I only quote what was wrote in JARs. John T and others are your real expert sources.
Dick W