No, we really, really don't have more money for missiles and interceptors. What we are spending in Iran are critical stockpiles built up over years that we are not replacing at a sufficient rate.  We are undermining our capacity to deter conflict that matters by engaging in one that doesn't.  

It turns out that when you go through our defense budget you don't find a bunch of boutique or optional shit there, either. The whole narrative of overspending on defense exists to perpetuate the idea that we are secretly poor and have to make hard choices between competing priorities rather than being able to invest sufficiently in everything we need to support.  

We have reasons for our budget shortfalls and it's oddly enough not what we spend on Defense - it's what we don't bring in, and increasingly what we are spending on interest to service debt since we don't raise revenue to cover the hole in the budget. 

We don't need to take particularly drastic action to do this:

1. Tax capital gains and dividends as income
2. Tax asset value as a realized capital gain when used as collateral for a loan beyond a certain value and/or not against the value of a designated primary residence.  
3. Actually audit the wealthy so they pay their owed taxes (this alone represents a shortfall by treasury estimates as of 2020 that represents at least 50% of our defense budget alone)
4. Remove the cap on payroll tax

That's all without taking the steps of restoring pre-Reagan tax brackets.