Most agencies have donors who are open to contact, so I would recommend finding an agency that is good and fits your needs (there are some who have more Asian donors, for instance). I think someone posted here a few weeks ago looking for agency recs; might scan back through the posts to see if you find some.
Once you have the agency, you can find the donor, and know where they are located. At that point, you can locate a clinic near them that serves your needs--there are usually several to choose from in an area, and most will have some sort of guarantee program. Since you are looking at agency donors, there is a significant possibility that you will go through more than one--they are not tested up-front, so there is greater risk that they may have a medical issue or just flake out.
If you have the money for it, there are people out there who can coordinate and manage the search for you, too, if you're feeling too overwhelmed.