I am aware from the post Where can I ask questions about the law, immigration, and other matters related to bureaucracy?, that there is no SE site to ask questions related US Immigration and US Tax. However are there any non SE QA sites available to ask questions related US Immigration and US tax?
Tax questions could probably be asked on Personal Finance and Money.
Here is a very good reference for asking Immigration questions:
I have seen a couple of my friends use it frequently.