Well, it would appear that there is good news and there is bad news. From what I understand (not being an attorney, mind you) you can request a discharge - which might spur the military into giving you the school you were guaranteed. But there is a catch, which I'll get to.
Assuming that you were guaranteed that MOS training in your enlistment contract, and did not get it, the applicable regulation would appear to be
AR 635-200 ch 7-16, "claims for unfulfilled enlistment commitment." According to the regulation you can file a DA Form 4187 requesting separation. (This is a standard form used for a number of "personnel action" requests).
Here is the kicker. Down in (4) in the regulation it states that such requests should be made "30 days after the defect was discovered or reasonably should have been discovered by the soldier." In other words, you can't just wait forever (or until it is handy for you) to make your request for discharge. You have 30 days from when you discovered, or "reasonably should have discovered", that the government was not going to fulfill your contract.
The Army *might* argue that since you haven't received your guaranteed training in a year and half, you should have long ago "reasonably" realized/discovered the problem and already made your request for discharge. Since you haven't, you have what is in effect a 'constructive enlistment' in which you have agreed (by going along with) to serve as an 11B.
Of course, you can argue that you were just being patient and it was not unreasonable for you to wait this long to complain. Your case might be bolstered if, for example, superiors told you your training was "in the works" or "being scheduled" or that the Guard is just Godawful slow about such things. You can also argue that you DID complain to your chain of command but either were not told, or were mistold, about the regulation and the 30 day period. ("Miscounseling" is a frequent, but difficult, defense).
I would talk to a JAG as soon as humanly possible. One problem you face is the timing of your request. If it is being done in the face of deployment the Army will claim your only reason for requesting discharge is the deployment, not the lack of training/MOS guaranteed. In addition, if you are deployed "pending a decision" or such, then your odds of getting approval will probably go down.
I'm not familiar enough with the Army or Guard to predict how this will likely turn out. If it were the Navy of a few years back, however, you would almost certainly have your discharge approved even if they put a "pro forma" paragraph about how they didn't *have* to but did so out of the goodness of their hearts. The Navy is meeting all its enlistment quotas, however....