Oh God, far too many! I am afraid this is an ever occuring problem, and with no easy solutions. The ones I know of are: try it out with your partner if she is willing to, for your sake. Find an online partner or a real live partner, with your wife's approval. Or - choose...
I was in that situation years back, and we ended up trying some things, and found that it did not work between us. But he was able to let me find a partner who could satisfy this need, outside of our relationship. It worked for 10 years.
I would definitly warn against Siggy's solution, to try to make your wife a sub behind her back, so to speak. IMO bdsm is based on honesty and communication, like any other relationship and, again IMO, trying to change the rules without admitting it is not something I think could ever work, in the long or the short run. If she has any sub gen at all, you should be able to do some careful and patient experiments quite honestly between you. If not, that kind of thing will not work, but might spark very angry responses.