Hi. I was actually looking to buy some seeds all at one place too. Most big companies charge alot for shipping, which could be spent on more seeds
Why not try ebay? I am actually going to buy some from there. They are pretty cheap and most have free shipping. You will probably find all 3 that you're looking for there
Ice plant can be grown by picking a piece out of someone elses yard and sticking it in dirt. Ice Plant is also really cheap as are Hibiscus plants at least the pink ones are...and easy to grow. The other colors don't do as well for me. I would not buy seeds for those two plants. I have both all over my yard. Haven't bought Mazuri yet. I guess I should, but it seems unnatural to me.
If you know where there is a Rose of Sharon tree, just go there in the Fall, and you can get hundreds of seeds. They look just like flower buds only they are brown. Each bud has a load of seeds in them. You can pull them off the tree or wait until the fall off. My tort loves the little sprouts that come up in the Spring.