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.
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.