How do I propagate Agave victoriae-reginae?
Agave is propagated by seed, offsets and tissue culture.
If it is your own plant that you want to propagate, you may have to wait twenty or thirty years for the plant to flower and provide seeds. You can, however, get Agave victoriae-reginae seed from J. L Hudson and others perhaps. Germinating it in a flat or container of sterile sand at 70-80F (20-25C) be would be a good approach. Given Agave's weird lifecycle, I would expect the germination to be inconsistent and to occur over a long period (several weeks). Xeric World Forums has an interesting discussion on Agave and Yucca germination (page four is the best part).
Agave also produces small plantlets next to the main plant in much the same way that Sempervivum does. These plantlets are called offsets. Agave victoriae-reginae is very slow growing, so it produces few offsets, but they may occur occasionally. The main plant can be lifted, spring or early autumn, when the temperatures are moderate, and the offsets can be detached from the main plant. Try to keep as many root as possible with the offset. Also, leave the offset out to dry until any cuts that you have made have callused over. Then plant. Be cautious to avoid overwatering. A good description of the procedure can be found at Mikes Exotics and Hardy Plants blog. I have never propagated Agave this way, but I have with Lewisia.