I'm making orgeat and it calls for 1/2 a tsp each of orange flower and rose water. I found the orange flower water in my cupboard and I don't have any store near me to get rose water. Would it be ok to just omit the rose water and use a tsp of orange flower water?
You *can*, but...
Orange blossom water can very easily overpower everything else in your syrup and even your cocktail, for that matter.
So I'd recommend going slow with it, taste-testing both the plain syrup and mixed into a cocktail (an army & navy has a bit less going on than a mai tai, but it's probably best to test with whatever cocktail you enjoy most.) You can always add a few more drops of orange blossom water.