Here in Pennsylvania, where we get 38-40" annual rainfall, I would say 5-6 tons of 1st cutting alfalfa haylage is common.  That is based on 60-65% moisture.  I would expect that 1st cutting irrigated alfalfa haylage in your area would be similar.  Unless you get a better number, I would use that as a starting point for planning.

I do want to say... I think your number of 35-40% moisture is too low. I think you will have trouble packing, and curing the haylage at that moisture level - unless you are planning to put it in an upright, oxygen-limiting silo.   For a bunker, I think 60-65% moisture is a better target moisture; if you are putting it on a pile, maybe figure on 65-70% moisture. If you are planning on 70% moisture, increase your expected yield accordingly.  If you are truly planning on 35-40% moisture, decrease your expected yield accordingly.

Those are my thoughts.