Not exactly. In theory you can also farm normal quests, many maps have a rare spawn which drops a R weapon most of the time. But it's not really worth your time. More realistically, if you grind Standard and Expert Disaster raids though, you should be getting SR weapons from those. If use 6 R weapons (worth 60 skill points) in one of those things, you'll make a SR weapon that gives 140 skill points. Effectively turning (35+60=)95 skill points into 140. Bonus, you also get T2 Cores from this farm, which is a huge choke for future stuff.
Even though you can slightly speed it up, remember that Grids simply take time. Have patience, and have fun!