This is something that gets easier as you become a more experienced tyer. The idea is to look at the fly and determine what the purpose of the material is in the fly. Once you understand what the reason for using that material is you can look at what you have that will have a similar effect. When you only have a few materials it is certainly harder to find something that will work. It is now hunting season so you should be gathering material by hunting or asking freinds who do hunt for the following items:
squirrel skins and tails (skin will substitute for hares mask in a pinch)
duck wings, flank feathers and CDC
deer hair and bucktail
skins from any upland bird (loose feathers and wings at least)
snowshoe rabbit feet and masks (that is your hares mask)
turkey tail and wing feathers (especially secondary wing feathers)
elk and moose if possible
just about anything else though I have given up on skunk which I just can't get the odor out of
If you're not sure what to keep from a given bird or animal just ask here
I can think of few acts more selfish than refusing a vaccination.