I just visited my local high-end nursery yesterday and was surprised to find they had several varieties of avocado trees in their greenhouses. They were in bud and looked pretty darn good. I'm sorry I can't remember which nursery they came from, but it was either Four Winds Growers or Monrovia. Either company should be able to tell you where in your area you can find a retailer, or maybe you can order one directly. If you're just interested in growing up some ornamental avocado plants, they're not hard to start from seed, there should be lots of propagation instruction online. Good luck! I have two in a pot that I started a couple of months ago and am currently trying to talk DH into one of the trees from the nursery.
If you want fruit it can take up to 7 years to produce. I have never heard of one producing in a pot? The other issue I have heard of is some avocados are hybrids. so the seed may not give you the fruit you are expecting it to produce? Since you seem to want it as an ornamental kind of thing I guess it dosnt matter?
Oh my, after eating an avocado, my grandmother would just stick it in dirt and there comes a tree. I do the same and have several of them in one pot. They are pretty and fast growing, I have never had one give fruit but I enjoy them. My problem is the mango, I can't get one to seed.
The plants are certainly easy to grow from seed. In fact, they often sprout in the compost. They make attractive trees, too. However, I just read that they often don't set fruit, even if you have two trees for cross-pollination. Here's a quote from this week's Berkeley Daily Planet:
"...in order to avoid the self-pollination that might weaken its progeny, the avocado has an extraordinary mechanism called dianthesis, which gives it a schedule of preparing its flower parts to yield or receive pollen either in the morning or the afternoon. If the tree's neighbor has the same schedule, no pollination can take place."