I buy mixed greens, green lettuce, red lettuce, romaine lettuce, radish greens, dandelion greens, kale, collards, radicchio, purple cabbage, and any other misc greens (gongura leaves, methi leaves, moringa leaves, …) that I can find in stores like Sprouts, Costco, Trader Joe's, farmers market and Indian grocery stores.

I do minimize high-oxalate leafy greens like spinach, chard and beet greens. Why? See Leafy Greens and Oxalates — guidelines by Dr Greger.

How many leafy greens? As many as possible! I try to make about 60% to 70% of my salad be leafy greens.