If you have documentation that these things occured within the first year of construction, you should be covered under the MA standard builder's warranty. If the builder is being un-responsive, I would consult with an attorney.
Just to clarify- a foundation leak usually is not a structural problem. 90% of the time. The water leak can be fixed for about $800 -$1000 by calling a foundation repair contractor.
If the builder is still in business- which is not a given as the weeks go by- they almost certainly have zero money available to pay to fix any of your issues, even if they are legit issues and original warranty problems. Check out how YOUR warranty is written in your P&S when you bought the place.
In a practical sense, if you have a family friend who is an attorney, you should have them write a letter to the builder in a harsh tone and then you will see the builder make the appropriate remedies- most likely. You have to stand out from the crowd. My guess is you're not the only former buyer who has been calling them with warranty issues.
Thanks, and good luck,
I would go to the association - and notify them in writing of the structural issues