if i'm understanding your question right, you're wanting to know where to purchase semen & embryos?
there are companies who specialize in semen sales. they have bulls of different breeds that you can choose from. here are a couple of links. i'm sure other people can add more.
if i remember right, you mentioned once that you weren't interested in herefords? that's really the only semen we order & we order pretty much everything through reed enterprises. they have semen and certificates on just about any hereford or polled hereford bull you could want.
we just call them & let them know what we want & they ship it ups to arrive on whatever day you want.
semen can also usually be purchased directly from owner(s) of whatever bull you're interested in using.
embryos can be purchased either through word of mouth private treaty or more commonly at production sales. many ranches will offer embryo lots along with their regular lots for sale.
We also have semen on 5 Longhorn bulls. Can see list at http://www.runningarrowlonghorns.com at "Breeding Program" option, then click on "Semen". Bulls are solid black, red roan, and red & white options.
http://www.ultimategenetics.com is a great site. Many breeds are well represented.
As far as embryos, I would probably guess that you would need to get those through the breeder probably. Some genetics companies will have them, but not all.
http://bullseyegenetics.com/ is a new site owned by Charles Levins. He has over 700 bulls available. All semen is sold at below list prices. He plans to have his sires listed online by this fall.
http://sementank.com is a place where you can showcase your featured sires and has some semen listed that is not available elsewhere. Also MVE semen tanks.