Hi Soshan and welcome to the forums!
There is no easy way to disable certain dates from being input like you want, but you can do this with code. To do this, double-click the date field, go to Data Validation tab, select OnBeforeChange event at the bottom, and then click edit form code. Insert code here (using examples found from searching this forum) to read the date that the user inserted. If it is not in the right time range, then add an error to the node and/or clear the value. Make sure to pop up a message letting the user know what you're doing.
You will probably want to add a note in your form to tell the users the dates they cannot enter.
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge