What would you recommend for quad weakness that causes difficulty standing from kneeling?

Various quad sets. Depending on your activity level and whether there is patella (kneecap) problems, there are many safe exercises for the quads. I do not recommend knee extension and knee flexion machines, which can make knee problems worse. I prefer straight leg raises, exercise bicycle, and gentle (slow) stairclimbing. Forcing yourself not to limp will also help. Lunges and squats are more difficult but effective.