Vitamin supp is as follows (for a 70-lb finishing lamb):
Vit A 1000 IU/day
Vit D 300 IU/day
Vit E 50 mg/day
Liquid versions are easiest but do whatever you can.
Yes, in the beginning, you'd feed a small handfull once in the morning, the next day, twice, morning and afternoon, then scale up slowly. Best is if you can use a self-feeder and the lamb will learn to eat out of that as well as whatever roughage is available. After a two weeks of transition you take the next week to essentially just fill the feeder and refill when needed. (Only do this if you can keep the feed free of rain, dirt and marauding critters; if not, feed twice daily--but try to move to self-feeding if possible.) If this is confusing feel free to wing it but keep in find that there needs to be a transition so as not to screw up the digestion of the lamb. That can cause problems.
If it is possible to get some other grains, do (barley in particular), but see if you can nab some molasses. Figure the molasses at about 20-25% of feed weight then mixed with water, moisten the feed with it before feeding.
Local people there might already have a good formula of local ingredients, if discoverable, that would work best for you if you are able to find out that sort of info.