I definitely reccomend Leo Schordje. He is on SlipperTalk and has some of the best sanderianums from small ones for $45 to 2 growth blooming sized ones for $125. He even sent a free P. gratrixianum seedling with my order. He has pictures of all the previous bloomed sanderianums and he could tell you when you can expect them to bloom and when they last bloomed. He is at
schordje.com and has more sanderianums than listed on his website. I got a 2 growth one for $125 and it had TONS of healthy roots.