Yeah, I've been refreshing for about an hour and not seeing any. I finally gave up and just took some other seeds, figuring that since they're permanent, I can get some later.
I'm not sure the algorithm that is used for the garden seeds. If the drops are random, then the fact that we have so many breeds would make anything more difficult to find. If the drops are based upon what's already in the wild (that is, if there are already a bunch of a type of seed, no more of that type gets dropped), then that algorithm would be better (more difficult for the programmer to calculate, of course), and there would be a more even distribution of all types of seeds.
I do NOT think that this sort of algorithm is in place, however. I was noticing in my refreshes that there was a predominance of certain kinds of seeds throughout the garden. At one point at one refresh, I had almost an entire page of just one breed! That indicates that the drops that are made to the garden are independent of what already exists, and I believe that this can eventually become a problem. It's like in Dragon Cave when we used to have so many common egg cave blockers. It looks like that's what's beginning to happen now.